release 1.3.0

final changelog edits for 1.3.0
Merge pull request #3295 from minrk/changelog-1.3
2025-10-07 18:14:10 +00:00 · 2020-12-11 12:07:55 +01:00 · 2020-12-11 12:07:06 +01:00 · 2020-12-11 12:02:15 +01:00 · 2020-12-11 09:39:28 +01:00 · 2020-12-11 13:15:13 +05:30
58 changed files with 1329 additions and 638 deletions
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -0,0 +1,225 @@
+# This is a GitHub workflow defining a set of jobs with a set of steps.
+# ref: https://docs.github.com/en/free-pro-team@latest/actions/reference/workflow-syntax-for-github-actions
+#
+name: Run tests
+
+# Trigger the workflow's on all PRs but only on pushed tags or commits to
+# main/master branch to avoid PRs developed in a GitHub fork's dedicated branch
+# to trigger.
+on:
+  pull_request:
+  push:
+
+defaults:
+  run:
+    # Declare bash be used by default in this workflow's "run" steps.
+    #
+    # NOTE: bash will by default run with:
+    #   --noprofile: Ignore ~/.profile etc.
+    #   --norc:      Ignore ~/.bashrc etc.
+    #   -e:          Exit directly on errors
+    #   -o pipefail: Don't mask errors from a command piped into another command
+    shell: bash
+
+env:
+  # UTF-8 content may be interpreted as ascii and causes errors without this.
+  LANG: C.UTF-8
+
+jobs:
+  # Run "pre-commit run --all-files"
+  pre-commit:
+    runs-on: ubuntu-20.04
+    timeout-minutes: 2
+
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+        with:
+          python-version: 3.8
+
+      # ref: https://github.com/pre-commit/action
+      - uses: pre-commit/action@v2.0.0
+      - name: Help message if pre-commit fail
+        if: ${{ failure() }}
+        run: |
+          echo "You can install pre-commit hooks to automatically run formatting"
+          echo "on each commit with:"
+          echo "    pre-commit install"
+          echo "or you can run by hand on staged files with"
+          echo "    pre-commit run"
+          echo "or after-the-fact on already committed files with"
+          echo "    pre-commit run --all-files"
+
+
+  # Run "pytest jupyterhub/tests" in various configurations
+  pytest:
+    runs-on: ubuntu-20.04
+    timeout-minutes: 10
+
+    strategy:
+      # Keep running even if one variation of the job fail
+      fail-fast: false
+      matrix:
+        # We run this job multiple times with different parameterization
+        # specified below, these parameters have no meaning on their own and
+        # gain meaning on how job steps use them.
+        #
+        # subdomain:
+        #   Tests everything when JupyterHub is configured to add routes for
+        #   users with dedicated subdomains like user1.jupyter.example.com
+        #   rather than jupyter.example.com/user/user1.
+        #
+        # db: [mysql/postgres]
+        #   Tests everything when JupyterHub works against a dedicated mysql or
+        #   postgresql server.
+        #
+        # jupyter_server:
+        #   Tests everything when the user instances are started with
+        #   jupyter_server instead of notebook.
+        #
+        # ssl:
+        #   Tests everything using internal SSL connections instead of
+        #   unencrypted HTTP
+        #
+        # main_dependencies:
+        #   Tests everything when the we use the latest available dependencies
+        #   from: ipytraitlets.
+        #
+        # NOTE: Since only the value of these parameters are presented in the
+        #       GitHub UI when the workflow run, we avoid using true/false as
+        #       values by instead duplicating the name to signal true.
+        include:
+          - python: "3.6"
+            oldest_dependencies: oldest_dependencies
+          - python: "3.6"
+            subdomain: subdomain
+          - python: "3.7"
+            db: mysql
+          - python: "3.7"
+            ssl: ssl
+          - python: "3.8"
+            db: postgres
+          - python: "3.8"
+            jupyter_server: jupyter_server
+          - python: "3.9"
+            main_dependencies: main_dependencies
+
+    steps:
+      # NOTE: In GitHub workflows, environment variables are set by writing
+      #       assignment statements to a file. They will be set in the following
+      #       steps as if would used `export MY_ENV=my-value`.
+      - name: Configure environment variables
+        run: |
+          if [ "${{ matrix.subdomain }}" != "" ]; then
+              echo "JUPYTERHUB_TEST_SUBDOMAIN_HOST=http://localhost.jovyan.org:8000" >> $GITHUB_ENV
+          fi
+          if [ "${{ matrix.db }}" == "mysql" ]; then
+              echo "MYSQL_HOST=127.0.0.1" >> $GITHUB_ENV
+              echo "JUPYTERHUB_TEST_DB_URL=mysql+mysqlconnector://root@127.0.0.1:3306/jupyterhub" >> $GITHUB_ENV
+          fi
+          if [ "${{ matrix.ssl }}" == "ssl" ]; then
+              echo "SSL_ENABLED=1" >> $GITHUB_ENV
+          fi
+          if [ "${{ matrix.db }}" == "postgres" ]; then
+              echo "PGHOST=127.0.0.1" >> $GITHUB_ENV
+              echo "PGUSER=test_user" >> $GITHUB_ENV
+              echo "PGPASSWORD=hub[test/:?" >> $GITHUB_ENV
+              echo "JUPYTERHUB_TEST_DB_URL=postgresql://test_user:hub%5Btest%2F%3A%3F@127.0.0.1:5432/jupyterhub" >> $GITHUB_ENV
+          fi
+          if [ "${{ matrix.jupyter_server }}" != "" ]; then
+              echo "JUPYTERHUB_SINGLEUSER_APP=jupyterhub.tests.mockserverapp.MockServerApp" >> $GITHUB_ENV
+          fi
+      - uses: actions/checkout@v2
+
+      # NOTE: actions/setup-node@v1 make use of a cache within the GitHub base
+      #       environment and setup in a fraction of a second.
+      - name: Install Node v14
+        uses: actions/setup-node@v1
+        with:
+          node-version: "14"
+      - name: Install Node dependencies
+        run: |
+          npm install
+          npm install -g configurable-http-proxy
+          npm list
+
+      # NOTE: actions/setup-python@v2 make use of a cache within the GitHub base
+      #       environment and setup in a fraction of a second.
+      - name: Install Python ${{ matrix.python }}
+        uses: actions/setup-python@v2
+        with:
+          python-version: ${{ matrix.python }}
+      - name: Install Python dependencies
+        run: |
+          pip install --upgrade pip
+          pip install --upgrade . -r dev-requirements.txt
+
+          if [ "${{ matrix.oldest_dependencies }}" != "" ]; then
+            # take any dependencies in requirements.txt such as tornado>=5.0
+            # and transform them to tornado==5.0 so we can run tests with
+            # the earliest-supported versions
+            cat requirements.txt | grep '>=' | sed -e 's@>=@==@g' > oldest-requirements.txt
+            pip install -r oldest-requirements.txt
+          fi
+
+          if [ "${{ matrix.main_dependencies }}" != "" ]; then
+              pip install git+https://github.com/ipython/traitlets#egg=traitlets --force
+          fi
+          if [ "${{ matrix.jupyter_server }}" != "" ]; then
+              pip uninstall notebook --yes
+              pip install jupyter_server
+          fi
+          if [ "${{ matrix.db }}" == "mysql" ]; then
+              pip install mysql-connector-python
+          fi
+          if [ "${{ matrix.db }}" == "postgres" ]; then
+              pip install psycopg2-binary
+          fi
+
+          pip freeze
+
+      # NOTE: If you need to debug this DB setup step, consider the following.
+      #
+      # 1. mysql/postgressql are database servers we start as docker containers,
+      #    and we use clients named mysql/psql.
+      #
+      # 2. When we start a database server we need to pass environment variables
+      #    explicitly as part of the `docker run` command. These environment
+      #    variables are named differently from the similarly named environment
+      #    variables used by the clients.
+      #
+      #    - mysql    server ref: https://hub.docker.com/_/mysql/
+      #    - mysql    client ref: https://dev.mysql.com/doc/refman/5.7/en/environment-variables.html
+      #    - postgres server ref: https://hub.docker.com/_/postgres/
+      #    - psql     client ref: https://www.postgresql.org/docs/9.5/libpq-envars.html
+      #
+      # 3. When we connect, they should use 127.0.0.1 rather than the
+      #    default way of connecting which leads to errors like below both for
+      #    mysql and postgresql unless we set MYSQL_HOST/PGHOST to 127.0.0.1.
+      #
+      #    - ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)
+      #
+      - name: Start a database server (${{ matrix.db }})
+        if: ${{ matrix.db }}
+        run: |
+          if [ "${{ matrix.db }}" == "mysql" ]; then
+              sudo apt-get update
+              sudo apt-get install -y mysql-client
+              DB=mysql bash ci/docker-db.sh
+              DB=mysql bash ci/init-db.sh
+          fi
+          if [ "${{ matrix.db }}" == "postgres" ]; then
+              sudo apt-get update
+              sudo apt-get install -y postgresql-client
+              DB=postgres bash ci/docker-db.sh
+              DB=postgres bash ci/init-db.sh
+          fi
+
+      - name: Run pytest
+        # FIXME: --color=yes explicitly set because:
+        #        https://github.com/actions/runner/issues/241
+        run: |
+          pytest -v --maxfail=2 --color=yes --cov=jupyterhub jupyterhub/tests
+      - name: Submit codecov report
+        run: |
+          codecov
--- a/.gitignore
+++ b/.gitignore
@@ -28,3 +28,4 @@ htmlcov
 .pytest_cache
 pip-wheel-metadata
 docs/source/reference/metrics.rst
+oldest-requirements.txt
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -4,7 +4,7 @@ repos:
  hooks:
  - id: reorder-python-imports
 - repo: https://github.com/psf/black
-  rev: 19.10b0
+  rev: 20.8b1
  hooks:
  - id: black
 - repo: https://github.com/pre-commit/pre-commit-hooks
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,120 +0,0 @@
-dist: bionic
-language: python
-cache:
-  - pip
-env:
-  global:
-    - MYSQL_HOST=127.0.0.1
-    - MYSQL_TCP_PORT=13306
-
-# request additional services for the jobs to access
-services:
-  - postgresql
-  - docker
-
-# install dependencies for running pytest (but not linting)
-before_install:
-  - set -e
-  - nvm install 6; nvm use 6
-  - npm install
-  - npm install -g configurable-http-proxy
-  - |
-    # setup database
-    if [[ $JUPYTERHUB_TEST_DB_URL == mysql* ]]; then
-      unset MYSQL_UNIX_PORT
-      DB=mysql bash ci/docker-db.sh
-      DB=mysql bash ci/init-db.sh
-      # FIXME: mysql-connector-python 8.0.16 incorrectly decodes bytes to str
-      # ref: https://bugs.mysql.com/bug.php?id=94944
-      pip install 'mysql-connector-python==8.0.11'
-    elif [[ $JUPYTERHUB_TEST_DB_URL == postgresql* ]]; then
-      psql -c "CREATE USER $PGUSER WITH PASSWORD '$PGPASSWORD';" -U postgres
-      DB=postgres bash ci/init-db.sh
-      pip install psycopg2-binary
-    fi
-
-# install general dependencies
-install:
-  - pip install --upgrade pip
-  - pip install --upgrade --pre -r dev-requirements.txt .
-  - |
-    if [[ "$MASTER_DEPENDENCIES" == "True" ]]; then
-       pip install git+https://github.com/ipython/traitlets#egg=traitlets --force
-    fi
-  - |
-    if [[ "$TEST" == "jupyter_server" ]]; then
-       pip uninstall notebook --yes
-       pip install jupyter_server
-    fi
-  - pip freeze
-
-# run tests
-script:
-  - pytest -v --maxfail=2 --cov=jupyterhub jupyterhub/tests
-
-# collect test coverage information
-after_success:
-  - codecov
-
-# list the jobs
-jobs:
-  include:
-    - name: autoformatting check
-      python: 3.6
-      # NOTE: It does not suffice to override to: null, [], or [""]. Travis will
-      #       fall back to the default if we do.
-      before_install: echo "Do nothing before install."
-      script:
-        - pre-commit run --all-files
-      after_success: echo "Do nothing after success."
-      after_failure:
-        - |
-          echo "You can install pre-commit hooks to automatically run formatting"
-          echo "on each commit with:"
-          echo "    pre-commit install"
-          echo "or you can run by hand on staged files with"
-          echo "    pre-commit run"
-          echo "or after-the-fact on already committed files with"
-          echo "    pre-commit run --all-files"
-    # When we run pytest, we want to run it with python>=3.5 as well as with
-    # various configurations. We increment the python version at the same time
-    # as we test new configurations in order to reduce the number of test jobs.
-    - name: python:3.5 + dist:xenial
-      python: 3.5
-      dist: xenial
-    - name: python:3.6 + subdomain
-      python: 3.6
-      env: JUPYTERHUB_TEST_SUBDOMAIN_HOST=http://localhost.jovyan.org:8000
-    - name: python:3.7 + mysql
-      python: 3.7
-      env:
-        - JUPYTERHUB_TEST_DB_URL=mysql+mysqlconnector://root@127.0.0.1:$MYSQL_TCP_PORT/jupyterhub
-    - name: python:3.8 + postgresql
-      python: 3.8
-      env:
-        - PGUSER=jupyterhub
-        - PGPASSWORD=hub[test/:?
-        # The password in url below is url-encoded with: urllib.parse.quote($PGPASSWORD, safe='')
-        - JUPYTERHUB_TEST_DB_URL=postgresql://jupyterhub:hub%5Btest%2F%3A%3F@127.0.0.1/jupyterhub
-    - name: python:3.8 + master dependencies
-      python: 3.8
-      env:
-        - PGUSER=jupyterhub
-        - PGPASSWORD=hub[test/:?
-        # The password in url below is url-encoded with: urllib.parse.quote($PGPASSWORD, safe='')
-        - JUPYTERHUB_TEST_DB_URL=postgresql://jupyterhub:hub%5Btest%2F%3A%3F@127.0.0.1/jupyterhub
-        - MASTER_DEPENDENCIES=True
-    - name: python:3.8 + jupyter_server
-      python: 3.8
-      env:
-        - TEST=jupyter_server
-        - JUPYTERHUB_SINGLEUSER_APP=jupyterhub.tests.mockserverapp.MockServerApp
-
-    - name: python:nightly
-      python: nightly
-  allow_failures:
-    - name: python:nightly
-    # https://github.com/jupyterhub/jupyterhub/issues/3141
-    # The latest traitlets is close to release so it should not fail
-    # - name: python:3.8 + master dependencies
-  fast_finish: true
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -1,7 +1,7 @@
 # Contributing to JupyterHub

 Welcome! As a [Jupyter](https://jupyter.org) project,
-you can follow the [Jupyter contributor guide](https://jupyter.readthedocs.io/en/latest/contributor/content-contributor.html).
+you can follow the [Jupyter contributor guide](https://jupyter.readthedocs.io/en/latest/contributing/content-contributor.html).

 Make sure to also follow [Project Jupyter's Code of Conduct](https://github.com/jupyter/governance/blob/master/conduct/code_of_conduct.md)
 for a friendly and welcoming collaborative environment.
--- a/README.md
+++ b/README.md
@@ -13,7 +13,7 @@
 [![Latest PyPI version](https://img.shields.io/pypi/v/jupyterhub?logo=pypi)](https://pypi.python.org/pypi/jupyterhub)
 [![Latest conda-forge version](https://img.shields.io/conda/vn/conda-forge/jupyterhub?logo=conda-forge)](https://www.npmjs.com/package/jupyterhub)
 [![Documentation build status](https://img.shields.io/readthedocs/jupyterhub?logo=read-the-docs)](https://jupyterhub.readthedocs.org/en/latest/)
-[![TravisCI build status](https://img.shields.io/travis/jupyterhub/jupyterhub/master?logo=travis)](https://travis-ci.org/jupyterhub/jupyterhub)
+[![TravisCI build status](https://img.shields.io/travis/com/jupyterhub/jupyterhub?logo=travis)](https://travis-ci.com/jupyterhub/jupyterhub)
 [![DockerHub build status](https://img.shields.io/docker/build/jupyterhub/jupyterhub?logo=docker&label=build)](https://hub.docker.com/r/jupyterhub/jupyterhub/tags)
 [![CircleCI build status](https://img.shields.io/circleci/build/github/jupyterhub/jupyterhub?logo=circleci)](https://circleci.com/gh/jupyterhub/jupyterhub)<!-- CircleCI Token: b5b65862eb2617b9a8d39e79340b0a6b816da8cc -->
 [![Test coverage of code](https://codecov.io/gh/jupyterhub/jupyterhub/branch/master/graph/badge.svg)](https://codecov.io/gh/jupyterhub/jupyterhub)
--- a/ci/docker-db.sh
+++ b/ci/docker-db.sh
@@ -1,59 +1,60 @@
 #!/usr/bin/env bash
-# source this file to setup postgres and mysql
-# for local testing (as similar as possible to docker)
+# The goal of this script is to start a database server as a docker container.
+#
+# Required environment variables:
+# - DB: The database server to start, either "postgres" or "mysql".
+#
+# - PGUSER/PGPASSWORD: For the creation of a postgresql user with associated
+#   password.

 set -eu

-export MYSQL_HOST=127.0.0.1
-export MYSQL_TCP_PORT=${MYSQL_TCP_PORT:-13306}
-export PGHOST=127.0.0.1
-NAME="hub-test-$DB"
-DOCKER_RUN="docker run -d --name $NAME"
+# Stop and remove any existing database container
+DOCKER_CONTAINER="hub-test-$DB"
+docker rm -f "$DOCKER_CONTAINER" 2>/dev/null || true

-docker rm -f "$NAME" 2>/dev/null || true
+# Prepare environment variables to startup and await readiness of either a mysql
+# or postgresql server.
+if [[ "$DB" == "mysql" ]]; then
+    # Environment variables can influence both the mysql server in the docker
+    # container and the mysql client.
+    #
+    # ref server: https://hub.docker.com/_/mysql/
+    # ref client: https://dev.mysql.com/doc/refman/5.7/en/setting-environment-variables.html
+    #
+    DOCKER_RUN_ARGS="-p 3306:3306 --env MYSQL_ALLOW_EMPTY_PASSWORD=1 mysql:5.7"
+    READINESS_CHECK="mysql --user root --execute \q"
+elif [[ "$DB" == "postgres" ]]; then
+    # Environment variables can influence both the postgresql server in the
+    # docker container and the postgresql client (psql).
+    #
+    # ref server: https://hub.docker.com/_/postgres/
+    # ref client: https://www.postgresql.org/docs/9.5/libpq-envars.html
+    #
+    # POSTGRES_USER / POSTGRES_PASSWORD will create a user on startup of the
+    # postgres server, but PGUSER and PGPASSWORD are the environment variables
+    # used by the postgresql client psql, so we configure the user based on how
+    # we want to connect.
+    #
+    DOCKER_RUN_ARGS="-p 5432:5432 --env "POSTGRES_USER=${PGUSER}" --env "POSTGRES_PASSWORD=${PGPASSWORD}" postgres:9.5"
+    READINESS_CHECK="psql --command \q"
+else
+    echo '$DB must be mysql or postgres'
+    exit 1
+fi

-case "$DB" in
-"mysql")
-  RUN_ARGS="-e MYSQL_ALLOW_EMPTY_PASSWORD=1 -p $MYSQL_TCP_PORT:3306 mysql:5.7"
-  CHECK="mysql --host $MYSQL_HOST --port $MYSQL_TCP_PORT --user root -e \q"
-  ;;
-"postgres")
-  RUN_ARGS="-p 5432:5432 postgres:9.5"
-  CHECK="psql --user postgres -c \q"
-  ;;
-*)
-  echo '$DB must be mysql or postgres'
-  exit 1
-esac
-
-$DOCKER_RUN $RUN_ARGS
+# Start the database server
+docker run --detach --name "$DOCKER_CONTAINER" $DOCKER_RUN_ARGS

+# Wait for the database server to start
 echo -n "waiting for $DB "
 for i in {1..60}; do
-  if $CHECK; then
-    echo 'done'
-    break
-  else
-    echo -n '.'
-    sleep 1
-  fi
+    if $READINESS_CHECK; then
+        echo 'done'
+        break
+    else
+        echo -n '.'
+        sleep 1
+    fi
 done
-$CHECK
-
-case "$DB" in
-"mysql")
-  ;;
-"postgres")
-  # create the user
-  psql --user postgres -c "CREATE USER $PGUSER WITH PASSWORD '$PGPASSWORD';"
-  ;;
-*)
-esac
-
-echo -e "
-Set these environment variables:
-
-    export MYSQL_HOST=127.0.0.1
-    export MYSQL_TCP_PORT=$MYSQL_TCP_PORT
-    export PGHOST=127.0.0.1
-"
+$READINESS_CHECK
--- a/ci/init-db.sh
+++ b/ci/init-db.sh
@@ -1,27 +1,26 @@
 #!/usr/bin/env bash
-# initialize jupyterhub databases for testing
+# The goal of this script is to initialize a running database server with clean
+# databases for use during tests.
+#
+# Required environment variables:
+# - DB: The database server to start, either "postgres" or "mysql".

 set -eu

-MYSQL="mysql --user root --host $MYSQL_HOST --port $MYSQL_TCP_PORT -e "
-PSQL="psql --user postgres -c "
-
-case "$DB" in
-"mysql")
-  EXTRA_CREATE='CHARACTER SET utf8 COLLATE utf8_general_ci'
-  SQL="$MYSQL"
-  ;;
-"postgres")
-  SQL="$PSQL"
-  ;;
-*)
-  echo '$DB must be mysql or postgres'
-  exit 1
-esac
+# Prepare env vars SQL_CLIENT and EXTRA_CREATE_DATABASE_ARGS
+if [[ "$DB" == "mysql" ]]; then
+    SQL_CLIENT="mysql --user root --execute "
+    EXTRA_CREATE_DATABASE_ARGS='CHARACTER SET utf8 COLLATE utf8_general_ci'
+elif [[ "$DB" == "postgres" ]]; then
+    SQL_CLIENT="psql --command "
+else
+    echo '$DB must be mysql or postgres'
+    exit 1
+fi

+# Configure a set of databases in the database server for upgrade tests
 set -x
-
 for SUFFIX in '' _upgrade_072 _upgrade_081 _upgrade_094; do
-    $SQL "DROP DATABASE jupyterhub${SUFFIX};" 2>/dev/null || true
-    $SQL "CREATE DATABASE jupyterhub${SUFFIX} ${EXTRA_CREATE:-};"
+    $SQL_CLIENT "DROP DATABASE jupyterhub${SUFFIX};" 2>/dev/null || true
+    $SQL_CLIENT "CREATE DATABASE jupyterhub${SUFFIX} ${EXTRA_CREATE_DATABASE_ARGS:-};"
 done
--- a/docs/rest-api.yml
+++ b/docs/rest-api.yml
@@ -79,6 +79,21 @@ paths:
  /users:
    get:
      summary: List users
+      parameters:
+        - name: state
+          in: query
+          required: false
+          type: string
+          enum: ["inactive", "active", "ready"]
+          description: |
+            Return only users who have servers in the given state.
+            If unspecified, return all users.
+
+            active: all users with any active servers (ready OR pending)
+            ready: all users who have any ready servers (running, not pending)
+            inactive: all users who have *no* active servers (complement of active)
+
+            Added in JupyterHub 1.3
      responses:
        '200':
          description: The Hub's user list
--- a/docs/source/changelog.md
+++ b/docs/source/changelog.md
--- a/docs/source/getting-started/institutional-faq.md
+++ b/docs/source/getting-started/institutional-faq.md
@@ -21,7 +21,7 @@ Here is a quick breakdown of these three tools:
 * **The Jupyter Notebook** is a document specification (the `.ipynb`) file that interweaves
  narrative text with code cells and their outputs. It is also a graphical interface
  that allows users to edit these documents. There are also several other graphical interfaces
-  that allow users to edit the `.ipynb` format (nteract, Jupyer Lab, Google Colab, Kaggle, etc).
+  that allow users to edit the `.ipynb` format (nteract, Jupyter Lab, Google Colab, Kaggle, etc).
 * **JupyterLab** is a flexible and extendible user interface for interactive computing. It
  has several extensions that are tailored for using Jupyter Notebooks, as well as extensions
  for other parts of the data science stack.
--- a/docs/source/getting-started/services-basics.md
+++ b/docs/source/getting-started/services-basics.md
@@ -5,7 +5,7 @@ that interacts with the Hub's REST API. A Service may perform a specific
 or action or task. For example, shutting down individuals' single user
 notebook servers that have been idle for some time is a good example of
 a task that could be automated by a Service. Let's look at how the
-[cull_idle_servers][] script can be used as a Service.
+[jupyterhub_idle_culler][] script can be used as a Service.

 ## Real-world example to cull idle servers

@@ -15,11 +15,11 @@ document will:
 - explain some basic information about API tokens
 - clarify that API tokens can be used to authenticate to
  single-user servers as of [version 0.8.0](../changelog)
- show how the [cull_idle_servers][] script can be:
+- show how the [jupyterhub_idle_culler][] script can be:
    - used in a Hub-managed service
    - run as a standalone script

-Both examples for `cull_idle_servers` will communicate tasks to the
+Both examples for `jupyterhub_idle_culler` will communicate tasks to the
 Hub via the REST API.

 ## API Token basics
@@ -78,17 +78,23 @@ single-user servers, and only cookies can be used for authentication.
 0.8 supports using JupyterHub API tokens to authenticate to single-user
 servers.

-## Configure `cull-idle` to run as a Hub-Managed Service
+## Configure the idle culler to run as a Hub-Managed Service
+
+Install the idle culler:
+
+```
+pip install jupyterhub-idle-culler
+```

 In `jupyterhub_config.py`, add the following dictionary for the
-`cull-idle` Service to the `c.JupyterHub.services` list:
+`idle-culler` Service to the `c.JupyterHub.services` list:

 ```python
 c.JupyterHub.services = [
    {
-        'name': 'cull-idle',
+        'name': 'idle-culler',
        'admin': True,
-        'command': [sys.executable, 'cull_idle_servers.py', '--timeout=3600'],
+        'command': [sys.executable, '-m', 'jupyterhub_idle_culler', '--timeout=3600'],
    }
 ]
 ```
@@ -101,21 +107,21 @@ where:

 ## Run `cull-idle` manually as a standalone script

-Now you can run your script, i.e. `cull_idle_servers`, by providing it
+Now you can run your script by providing it
 the API token and it will authenticate through the REST API to
 interact with it.

-This will run `cull-idle` manually. `cull-idle` can be run as a standalone
+This will run the idle culler service manually. It can be run as a standalone
 script anywhere with access to the Hub, and will periodically check for idle
 servers and shut them down via the Hub's REST API. In order to shutdown the
 servers, the token given to cull-idle must have admin privileges.

 Generate an API token and store it in the `JUPYTERHUB_API_TOKEN` environment
-variable. Run `cull_idle_servers.py` manually.
+variable. Run `jupyterhub_idle_culler` manually.

 ```bash
    export JUPYTERHUB_API_TOKEN='token'
-    python3 cull_idle_servers.py [--timeout=900] [--url=http://127.0.0.1:8081/hub/api]
+    python -m jupyterhub_idle_culler [--timeout=900] [--url=http://127.0.0.1:8081/hub/api]
 ```

-[cull_idle_servers]: https://github.com/jupyterhub/jupyterhub/blob/master/examples/cull-idle/cull_idle_servers.py
+[jupyterhub_idle_culler]: https://github.com/jupyterhub/jupyterhub-idle-culler
--- a/docs/source/reference/authenticators.md
+++ b/docs/source/reference/authenticators.md
@@ -235,10 +235,9 @@ to Spawner environment:

 ```python
 class MyAuthenticator(Authenticator):
-    @gen.coroutine
-    def authenticate(self, handler, data=None):
-        username = yield identify_user(handler, data)
-        upstream_token = yield token_for_user(username)
+    async def authenticate(self, handler, data=None):
+        username = await identify_user(handler, data)
+        upstream_token = await token_for_user(username)
        return {
            'name': username,
            'auth_state': {
@@ -246,10 +245,9 @@ class MyAuthenticator(Authenticator):
            },
        }

-    @gen.coroutine
-    def pre_spawn_start(self, user, spawner):
+    async def pre_spawn_start(self, user, spawner):
        """Pass upstream_token to spawner via environment variable"""
-        auth_state = yield user.get_auth_state()
+        auth_state = await user.get_auth_state()
        if not auth_state:
            # auth_state not enabled
            return
--- a/docs/source/reference/config-proxy.md
+++ b/docs/source/reference/config-proxy.md
@@ -86,6 +86,7 @@ server {
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection $connection_upgrade;
+        proxy_set_header X-Scheme $scheme;

        proxy_buffering off;
    }
--- a/docs/source/reference/services.md
+++ b/docs/source/reference/services.md
@@ -50,7 +50,7 @@ A Service may have the following properties:

 If a service is also to be managed by the Hub, it has a few extra options:

- `command: (str/Popen list`) - Command for JupyterHub to spawn the service.
+- `command: (str/Popen list)` - Command for JupyterHub to spawn the service.
      - Only use this if the service should be a subprocess.
      - If command is not specified, the Service is assumed to be managed
        externally.
@@ -91,9 +91,9 @@ This example would be configured as follows in `jupyterhub_config.py`:
 ```python
 c.JupyterHub.services = [
    {
-        'name': 'cull-idle',
+        'name': 'idle-culler',
        'admin': True,
-        'command': [sys.executable, '/path/to/cull-idle.py', '--timeout']
+        'command': [sys.executable, '-m', 'jupyterhub_idle_culler', '--timeout=3600']
    }
 ]
 ```
@@ -123,15 +123,14 @@ For the previous 'cull idle' Service example, these environment variables
 would be passed to the Service when the Hub starts the 'cull idle' Service:

 ```bash
-JUPYTERHUB_SERVICE_NAME: 'cull-idle'
+JUPYTERHUB_SERVICE_NAME: 'idle-culler'
 JUPYTERHUB_API_TOKEN: API token assigned to the service
 JUPYTERHUB_API_URL: http://127.0.0.1:8080/hub/api
 JUPYTERHUB_BASE_URL: https://mydomain[:port]
-JUPYTERHUB_SERVICE_PREFIX: /services/cull-idle/
+JUPYTERHUB_SERVICE_PREFIX: /services/idle-culler/
 ```

-See the JupyterHub GitHub repo for additional information about the
-[`cull-idle` example](https://github.com/jupyterhub/jupyterhub/tree/master/examples/cull-idle).
+See the GitHub repo for additional information about the [jupyterhub_idle_culler][].

 ## Externally-Managed Services

@@ -340,7 +339,7 @@ and taking note of the following process:

    ```python
    r = requests.get(
-        '/'.join((["http://127.0.0.1:8081/hub/api",
+        '/'.join(["http://127.0.0.1:8081/hub/api",
                   "authorizations/cookie/jupyterhub-services",
                   quote(encrypted_cookie, safe=''),
        ]),
@@ -376,3 +375,4 @@ section on securing the notebook viewer.
 [HubAuth.user_for_token]: ../api/services.auth.html#jupyterhub.services.auth.HubAuth.user_for_token
 [HubAuthenticated]: ../api/services.auth.html#jupyterhub.services.auth.HubAuthenticated
 [nbviewer example]: https://github.com/jupyter/nbviewer#securing-the-notebook-viewer
+[jupyterhub_idle_culler]: https://github.com/jupyterhub/jupyterhub-idle-culler
--- a/examples/service-announcement/README.md
+++ b/examples/service-announcement/README.md
@@ -27,7 +27,7 @@ that environment variable is set or `/` if it is not.
 Admin users can set the announcement text with an API token:

    $ curl -X POST -H "Authorization: token <token>"                        \
-        -d "{'announcement':'JupyterHub will be upgraded on August 14!'}"   \
+        -d '{"announcement":"JupyterHub will be upgraded on August 14!"}'   \
        https://.../services/announcement

 Anyone can read the announcement:
--- a/jupyterhub/_version.py
+++ b/jupyterhub/_version.py
@@ -4,9 +4,9 @@

 version_info = (
    1,
-    2,
+    3,
    0,
-    "b1",  # release (b1, rc1, or "" for final or dev)
+    "",  # release (b1, rc1, or "" for final or dev)
    # "dev",  # dev or nothing for beta/rc/stable releases
 )

--- a/jupyterhub/apihandlers/auth.py
+++ b/jupyterhub/apihandlers/auth.py
@@ -215,7 +215,8 @@ class OAuthAuthorizeHandler(OAuthHandler, BaseHandler):
            # it's the user's own server
            oauth_client.identifier in own_oauth_client_ids
            # or it's in the global no-confirm list
-            or oauth_client.identifier in self.settings.get('oauth_no_confirm', set())
+            or oauth_client.identifier
+            in self.settings.get('oauth_no_confirm_list', set())
        ):
            return False
        # default: require confirmation
@@ -252,7 +253,7 @@ class OAuthAuthorizeHandler(OAuthHandler, BaseHandler):
            # Render oauth 'Authorize application...' page
            auth_state = await self.current_user.get_auth_state()
            self.write(
-                self.render_template(
+                await self.render_template(
                    "oauth.html",
                    auth_state=auth_state,
                    scopes=scopes,
@@ -274,9 +275,26 @@ class OAuthAuthorizeHandler(OAuthHandler, BaseHandler):
        uri, http_method, body, headers = self.extract_oauth_params()
        referer = self.request.headers.get('Referer', 'no referer')
        full_url = self.request.full_url()
-        if referer != full_url:
+        # trim protocol, which cannot be trusted with multiple layers of proxies anyway
+        # Referer is set by browser, but full_url can be modified by proxy layers to appear as http
+        # when it is actually https
+        referer_proto, _, stripped_referer = referer.partition("://")
+        referer_proto = referer_proto.lower()
+        req_proto, _, stripped_full_url = full_url.partition("://")
+        req_proto = req_proto.lower()
+        if referer_proto != req_proto:
+            self.log.warning("Protocol mismatch: %s != %s", referer, full_url)
+            if req_proto == "https":
+                # insecure origin to secure target is not allowed
+                raise web.HTTPError(
+                    403, "Not allowing authorization form submitted from insecure page"
+                )
+        if stripped_referer != stripped_full_url:
            # OAuth post must be made to the URL it came from
-            self.log.error("OAuth POST from %s != %s", referer, full_url)
+            self.log.error("Original OAuth POST from %s != %s", referer, full_url)
+            self.log.error(
+                "Stripped OAuth POST from %s != %s", stripped_referer, stripped_full_url
+            )
            raise web.HTTPError(
                403, "Authorization form must be sent from authorization page"
            )
--- a/jupyterhub/apihandlers/hub.py
+++ b/jupyterhub/apihandlers/hub.py
@@ -16,9 +16,9 @@ class ShutdownAPIHandler(APIHandler):
    @admin_only
    def post(self):
        """POST /api/shutdown triggers a clean shutdown
-        
+
        POST (JSON) parameters:
-        
+
        - servers: specify whether single-user servers should be terminated
        - proxy: specify whether the proxy should be terminated
        """
@@ -57,7 +57,7 @@ class RootAPIHandler(APIHandler):
        """GET /api/ returns info about the Hub and its API.

        It is not an authenticated endpoint.
-        
+
        For now, it just returns the version of JupyterHub itself.
        """
        data = {'version': __version__}
@@ -70,7 +70,7 @@ class InfoAPIHandler(APIHandler):
        """GET /api/info returns detailed info about the Hub and its API.

        It is not an authenticated endpoint.
-        
+
        For now, it just returns the version of JupyterHub itself.
        """

--- a/jupyterhub/apihandlers/users.py
+++ b/jupyterhub/apihandlers/users.py
@@ -9,6 +9,7 @@ from datetime import timezone

 from async_generator import aclosing
 from dateutil.parser import parse as parse_date
+from sqlalchemy import func
 from tornado import web
 from tornado.iostream import StreamClosedError

@@ -35,15 +36,69 @@ class SelfAPIHandler(APIHandler):
            user = self.get_current_user_oauth_token()
        if user is None:
            raise web.HTTPError(403)
-        self.write(json.dumps(self.user_model(user)))
+        if isinstance(user, orm.Service):
+            model = self.service_model(user)
+        else:
+            model = self.user_model(user)
+        self.write(json.dumps(model))


 class UserListAPIHandler(APIHandler):
+    def _user_has_ready_spawner(self, orm_user):
+        """Return True if a user has *any* ready spawners
+
+        Used for filtering from active -> ready
+        """
+        user = self.users[orm_user]
+        return any(spawner.ready for spawner in user.spawners.values())
+
    @admin_only
    def get(self):
+        state_filter = self.get_argument("state", None)
+
+        # post_filter
+        post_filter = None
+
+        if state_filter in {"active", "ready"}:
+            # only get users with active servers
+            # an 'active' Spawner has a server record in the database
+            # which means Spawner.server != None
+            # it may still be in a pending start/stop state.
+            # join filters out users with no Spawners
+            query = (
+                self.db.query(orm.User)
+                # join filters out any Users with no Spawners
+                .join(orm.Spawner)
+                # this implicitly gets Users with *any* active server
+                .filter(orm.Spawner.server != None)
+            )
+            if state_filter == "ready":
+                # have to post-process query results because active vs ready
+                # can only be distinguished with in-memory Spawner properties
+                post_filter = self._user_has_ready_spawner
+
+        elif state_filter == "inactive":
+            # only get users with *no* active servers
+            # as opposed to users with *any inactive servers*
+            # this is the complement to the above query.
+            # how expensive is this with lots of servers?
+            query = (
+                self.db.query(orm.User)
+                .outerjoin(orm.Spawner)
+                .outerjoin(orm.Server)
+                .group_by(orm.User.id)
+                .having(func.count(orm.Server.id) == 0)
+            )
+        elif state_filter:
+            raise web.HTTPError(400, "Unrecognized state filter: %r" % state_filter)
+        else:
+            # no filter, return all users
+            query = self.db.query(orm.User)
+
        data = [
            self.user_model(u, include_servers=True, include_state=True)
-            for u in self.db.query(orm.User)
+            for u in query
+            if (post_filter is None or post_filter(u))
        ]
        self.write(json.dumps(data))

--- a/jupyterhub/app.py
+++ b/jupyterhub/app.py
@@ -29,6 +29,14 @@ from urllib.parse import urlunparse
 if sys.version_info[:2] < (3, 3):
    raise ValueError("Python < 3.3 not supported: %s" % sys.version)

+# For compatibility with python versions 3.6 or earlier.
+# asyncio.Task.all_tasks() is fully moved to asyncio.all_tasks() starting with 3.9. Also applies to current_task.
+try:
+    asyncio_all_tasks = asyncio.all_tasks
+    asyncio_current_task = asyncio.current_task
+except AttributeError as e:
+    asyncio_all_tasks = asyncio.Task.all_tasks
+    asyncio_current_task = asyncio.Task.current_task

 from dateutil.parser import parse as parse_date
 from jinja2 import Environment, FileSystemLoader, PrefixLoader, ChoiceLoader
@@ -77,6 +85,7 @@ from .user import UserDict
 from .oauth.provider import make_provider
 from ._data import DATA_FILES_PATH
 from .log import CoroutineLogFormatter, log_request
+from .pagination import Pagination
 from .proxy import Proxy, ConfigurableHTTPProxy
 from .traitlets import URLPrefix, Command, EntryPointType, Callable
 from .utils import (
@@ -279,7 +288,7 @@ class JupyterHub(Application):

    @default('classes')
    def _load_classes(self):
-        classes = [Spawner, Authenticator, CryptKeeper]
+        classes = [Spawner, Authenticator, CryptKeeper, Pagination]
        for name, trait in self.traits(config=True).items():
            # load entry point groups into configurable class list
            # so that they show up in config files, etc.
@@ -2119,7 +2128,7 @@ class JupyterHub(Application):
            self.log.debug(
                "Awaiting checks for %i possibly-running spawners", len(check_futures)
            )
-            await gen.multi(check_futures)
+            await asyncio.gather(*check_futures)
        db.commit()

        # only perform this query if we are going to log it
@@ -2186,7 +2195,7 @@ class JupyterHub(Application):
    def init_tornado_settings(self):
        """Set up the tornado settings dict."""
        base_url = self.hub.base_url
-        jinja_options = dict(autoescape=True)
+        jinja_options = dict(autoescape=True, enable_async=True)
        jinja_options.update(self.jinja_environment_options)
        base_path = self._template_paths_default()[0]
        if base_path not in self.template_paths:
@@ -2198,6 +2207,14 @@ class JupyterHub(Application):
            ]
        )
        jinja_env = Environment(loader=loader, **jinja_options)
+        # We need a sync jinja environment too, for the times we *must* use sync
+        # code - particularly in RequestHandler.write_error. Since *that*
+        # is called from inside the asyncio event loop, we can't actulaly just
+        # schedule it on the loop - without starting another thread with its
+        # own loop, which seems not worth the trouble. Instead, we create another
+        # environment, exactly like this one, but sync
+        del jinja_options['enable_async']
+        jinja_env_sync = Environment(loader=loader, **jinja_options)

        login_url = url_path_join(base_url, 'login')
        logout_url = self.authenticator.logout_url(base_url)
@@ -2244,6 +2261,7 @@ class JupyterHub(Application):
            template_path=self.template_paths,
            template_vars=self.template_vars,
            jinja2_env=jinja_env,
+            jinja2_env_sync=jinja_env_sync,
            version_hash=version_hash,
            subdomain_host=self.subdomain_host,
            domain=self.domain,
@@ -2807,9 +2825,7 @@ class JupyterHub(Application):
    async def shutdown_cancel_tasks(self, sig):
        """Cancel all other tasks of the event loop and initiate cleanup"""
        self.log.critical("Received signal %s, initiating shutdown...", sig.name)
-        tasks = [
-            t for t in asyncio.Task.all_tasks() if t is not asyncio.Task.current_task()
-        ]
+        tasks = [t for t in asyncio_all_tasks() if t is not asyncio_current_task()]

        if tasks:
            self.log.debug("Cancelling pending tasks")
@@ -2822,7 +2838,7 @@ class JupyterHub(Application):
            except StopAsyncIteration as e:
                self.log.error("Caught StopAsyncIteration Exception", exc_info=True)

-            tasks = [t for t in asyncio.Task.all_tasks()]
+            tasks = [t for t in asyncio_all_tasks()]
            for t in tasks:
                self.log.debug("Task status: %s", t)
        await self.cleanup()
--- a/jupyterhub/auth.py
+++ b/jupyterhub/auth.py
@@ -101,7 +101,10 @@ class Authenticator(LoggingConfigurable):
        """
    ).tag(config=True)

-    whitelist = Set(help="Deprecated, use `Authenticator.allowed_users`", config=True,)
+    whitelist = Set(
+        help="Deprecated, use `Authenticator.allowed_users`",
+        config=True,
+    )

    allowed_users = Set(
        help="""
@@ -715,7 +718,9 @@ for _old_name, _new_name, _version in [
    ("check_blacklist", "check_blocked_users", "1.2"),
 ]:
    setattr(
-        Authenticator, _old_name, _deprecated_method(_old_name, _new_name, _version),
+        Authenticator,
+        _old_name,
+        _deprecated_method(_old_name, _new_name, _version),
    )


@@ -778,7 +783,9 @@ class LocalAuthenticator(Authenticator):
        """
    ).tag(config=True)

-    group_whitelist = Set(help="""DEPRECATED: use allowed_groups""",).tag(config=True)
+    group_whitelist = Set(
+        help="""DEPRECATED: use allowed_groups""",
+    ).tag(config=True)

    allowed_groups = Set(
        help="""
--- a/jupyterhub/handlers/base.py
+++ b/jupyterhub/handlers/base.py
@@ -40,6 +40,7 @@ from ..metrics import SERVER_STOP_DURATION_SECONDS
 from ..metrics import ServerPollStatus
 from ..metrics import ServerSpawnStatus
 from ..metrics import ServerStopStatus
+from ..metrics import TOTAL_USERS
 from ..objects import Server
 from ..spawner import LocalProcessSpawner
 from ..user import User
@@ -453,6 +454,7 @@ class BaseHandler(RequestHandler):
            # not found, create and register user
            u = orm.User(name=username)
            self.db.add(u)
+            TOTAL_USERS.inc()
            self.db.commit()
            user = self._user_from_orm(u)
        return user
@@ -489,7 +491,7 @@ class BaseHandler(RequestHandler):
        self.clear_cookie(
            'jupyterhub-services',
            path=url_path_join(self.base_url, 'services'),
-            **kwargs
+            **kwargs,
        )
        # Reset _jupyterhub_user
        self._jupyterhub_user = None
@@ -634,6 +636,12 @@ class BaseHandler(RequestHandler):
                next_url,
            )

+        # this is where we know if next_url is coming from ?next= param or we are using a default url
+        if next_url:
+            next_url_from_param = True
+        else:
+            next_url_from_param = False
+
        if not next_url:
            # custom default URL, usually passed because user landed on that page but was not logged in
            if default:
@@ -659,7 +667,10 @@ class BaseHandler(RequestHandler):
            else:
                next_url = url_path_join(self.hub.base_url, 'home')

-        next_url = self.append_query_parameters(next_url, exclude=['next'])
+        if not next_url_from_param:
+            # when a request made with ?next=... assume all the params have already been encoded
+            # otherwise, preserve params from the current request across the redirect
+            next_url = self.append_query_parameters(next_url, exclude=['next'])
        return next_url

    def append_query_parameters(self, url, exclude=None):
@@ -1156,16 +1167,36 @@ class BaseHandler(RequestHandler):
            "<a href='{home}'>home page</a>.".format(home=home)
        )

-    def get_template(self, name):
-        """Return the jinja template object for a given name"""
-        return self.settings['jinja2_env'].get_template(name)
+    def get_template(self, name, sync=False):
+        """
+        Return the jinja template object for a given name

-    def render_template(self, name, **ns):
+        If sync is True, we return a Template that is compiled without async support.
+        Only those can be used in synchronous code.
+
+        If sync is False, we return a Template that is compiled with async support
+        """
+        if sync:
+            key = 'jinja2_env_sync'
+        else:
+            key = 'jinja2_env'
+        return self.settings[key].get_template(name)
+
+    def render_template(self, name, sync=False, **ns):
+        """
+        Render jinja2 template
+
+        If sync is set to True, we return an awaitable
+        If sync is set to False, we render the template & return a string
+        """
        template_ns = {}
        template_ns.update(self.template_namespace)
        template_ns.update(ns)
-        template = self.get_template(name)
-        return template.render(**template_ns)
+        template = self.get_template(name, sync)
+        if sync:
+            return template.render(**template_ns)
+        else:
+            return template.render_async(**template_ns)

    @property
    def template_namespace(self):
@@ -1240,17 +1271,19 @@ class BaseHandler(RequestHandler):
            # Content-Length must be recalculated.
            self.clear_header('Content-Length')

-        # render the template
+        # render_template is async, but write_error can't be!
+        # so we run it sync here, instead of making a sync version of render_template
+
        try:
-            html = self.render_template('%s.html' % status_code, **ns)
+            html = self.render_template('%s.html' % status_code, sync=True, **ns)
        except TemplateNotFound:
            self.log.debug("No template for %d", status_code)
            try:
-                html = self.render_template('error.html', **ns)
+                html = self.render_template('error.html', sync=True, **ns)
            except:
                # In this case, any side effect must be avoided.
                ns['no_spawner_check'] = True
-                html = self.render_template('error.html', **ns)
+                html = self.render_template('error.html', sync=True, **ns)

        self.write(html)

@@ -1454,10 +1487,14 @@ class UserUrlHandler(BaseHandler):

        # if request is expecting JSON, assume it's an API request and fail with 503
        # because it won't like the redirect to the pending page
-        if get_accepted_mimetype(
-            self.request.headers.get('Accept', ''),
-            choices=['application/json', 'text/html'],
-        ) == 'application/json' or 'api' in user_path.split('/'):
+        if (
+            get_accepted_mimetype(
+                self.request.headers.get('Accept', ''),
+                choices=['application/json', 'text/html'],
+            )
+            == 'application/json'
+            or 'api' in user_path.split('/')
+        ):
            self._fail_api_request(user_name, server_name)
            return

@@ -1483,7 +1520,7 @@ class UserUrlHandler(BaseHandler):
        self.set_status(503)

        auth_state = await user.get_auth_state()
-        html = self.render_template(
+        html = await self.render_template(
            "not_running.html",
            user=user,
            server_name=server_name,
@@ -1538,7 +1575,7 @@ class UserUrlHandler(BaseHandler):
        if redirects:
            self.log.warning("Redirect loop detected on %s", self.request.uri)
            # add capped exponential backoff where cap is 10s
-            await gen.sleep(min(1 * (2 ** redirects), 10))
+            await asyncio.sleep(min(1 * (2 ** redirects), 10))
            # rewrite target url with new `redirects` query value
            url_parts = urlparse(target)
            query_parts = parse_qs(url_parts.query)
--- a/jupyterhub/handlers/login.py
+++ b/jupyterhub/handlers/login.py
@@ -72,14 +72,14 @@ class LogoutHandler(BaseHandler):
        Override this function to set a custom logout page.
        """
        if self.authenticator.auto_login:
-            html = self.render_template('logout.html')
+            html = await self.render_template('logout.html')
            self.finish(html)
        else:
            self.redirect(self.settings['login_url'], permanent=False)

    async def get(self):
        """Log the user out, call the custom action, forward the user
-            to the logout page
+        to the logout page
        """
        await self.default_handle_logout()
        await self.handle_logout()
@@ -132,7 +132,7 @@ class LoginHandler(BaseHandler):
                    self.redirect(auto_login_url)
                return
            username = self.get_argument('username', default='')
-            self.finish(self._render(username=username))
+            self.finish(await self._render(username=username))

    async def post(self):
        # parse the arguments dict
@@ -149,7 +149,7 @@ class LoginHandler(BaseHandler):
            self._jupyterhub_user = user
            self.redirect(self.get_next_url(user))
        else:
-            html = self._render(
+            html = await self._render(
                login_error='Invalid username or password', username=data['username']
            )
            self.finish(html)
--- a/jupyterhub/handlers/pages.py
+++ b/jupyterhub/handlers/pages.py
@@ -40,11 +40,15 @@ class RootHandler(BaseHandler):
    def get(self):
        user = self.current_user
        if self.default_url:
-            url = self.default_url
+            # As set in jupyterhub_config.py
+            if callable(self.default_url):
+                url = self.default_url(self)
+            else:
+                url = self.default_url
        elif user:
            url = self.get_next_url(user)
        else:
-            url = self.settings['login_url']
+            url = url_concat(self.settings["login_url"], dict(next=self.request.uri))
        self.redirect(url)


@@ -67,7 +71,7 @@ class HomeHandler(BaseHandler):
            url = url_path_join(self.hub.base_url, 'spawn', user.escaped_name)

        auth_state = await user.get_auth_state()
-        html = self.render_template(
+        html = await self.render_template(
            'home.html',
            auth_state=auth_state,
            user=user,
@@ -94,7 +98,7 @@ class SpawnHandler(BaseHandler):

    async def _render_form(self, for_user, spawner_options_form, message=''):
        auth_state = await for_user.get_auth_state()
-        return self.render_template(
+        return await self.render_template(
            'spawn.html',
            for_user=for_user,
            auth_state=auth_state,
@@ -378,7 +382,7 @@ class SpawnPendingHandler(BaseHandler):
                self.hub.base_url, "spawn", user.escaped_name, server_name
            )
            self.set_status(500)
-            html = self.render_template(
+            html = await self.render_template(
                "not_running.html",
                user=user,
                auth_state=auth_state,
@@ -402,7 +406,7 @@ class SpawnPendingHandler(BaseHandler):
                page = "stop_pending.html"
            else:
                page = "spawn_pending.html"
-            html = self.render_template(
+            html = await self.render_template(
                page,
                user=user,
                spawner=spawner,
@@ -429,7 +433,7 @@ class SpawnPendingHandler(BaseHandler):
            spawn_url = url_path_join(
                self.hub.base_url, "spawn", user.escaped_name, server_name
            )
-            html = self.render_template(
+            html = await self.render_template(
                "not_running.html",
                user=user,
                auth_state=auth_state,
@@ -453,7 +457,8 @@ class AdminHandler(BaseHandler):
    @web.authenticated
    @admin_only
    async def get(self):
-        page, per_page, offset = Pagination.get_page_args(self)
+        pagination = Pagination(url=self.request.uri, config=self.config)
+        page, per_page, offset = pagination.get_page_args(self)

        available = {'name', 'admin', 'running', 'last_activity'}
        default_sort = ['admin', 'name']
@@ -509,13 +514,10 @@ class AdminHandler(BaseHandler):
        for u in users:
            running.extend(s for s in u.spawners.values() if s.active)

-        total = self.db.query(orm.User.id).count()
-        pagination = Pagination(
-            url=self.request.uri, total=total, page=page, per_page=per_page,
-        )
+        pagination.total = self.db.query(orm.User.id).count()

        auth_state = await self.current_user.get_auth_state()
-        html = self.render_template(
+        html = await self.render_template(
            'admin.html',
            current_user=self.current_user,
            auth_state=auth_state,
@@ -605,7 +607,7 @@ class TokenPageHandler(BaseHandler):
        oauth_clients = sorted(oauth_clients, key=sort_key, reverse=True)

        auth_state = await self.current_user.get_auth_state()
-        html = self.render_template(
+        html = await self.render_template(
            'token.html',
            api_tokens=api_tokens,
            oauth_clients=oauth_clients,
@@ -617,7 +619,7 @@ class TokenPageHandler(BaseHandler):
 class ProxyErrorHandler(BaseHandler):
    """Handler for rendering proxy error pages"""

-    def get(self, status_code_s):
+    async def get(self, status_code_s):
        status_code = int(status_code_s)
        status_message = responses.get(status_code, 'Unknown HTTP Error')
        # build template namespace
@@ -641,10 +643,10 @@ class ProxyErrorHandler(BaseHandler):
        self.set_header('Content-Type', 'text/html')
        # render the template
        try:
-            html = self.render_template('%s.html' % status_code, **ns)
+            html = await self.render_template('%s.html' % status_code, **ns)
        except TemplateNotFound:
            self.log.debug("No template for %d", status_code)
-            html = self.render_template('error.html', **ns)
+            html = await self.render_template('error.html', **ns)

        self.write(html)

--- a/jupyterhub/handlers/static.py
+++ b/jupyterhub/handlers/static.py
@@ -7,7 +7,7 @@ from tornado.web import StaticFileHandler

 class CacheControlStaticFilesHandler(StaticFileHandler):
    """StaticFileHandler subclass that sets Cache-Control: no-cache without `?v=`
-    
+
    rather than relying on default browser cache behavior.
    """

--- a/jupyterhub/metrics.py
+++ b/jupyterhub/metrics.py
@@ -3,9 +3,9 @@ Prometheus metrics exported by JupyterHub

 Read https://prometheus.io/docs/practices/naming/ for naming
 conventions for metrics & labels. We generally prefer naming them
-`<noun>_<verb>_<type_suffix>`. So a histogram that's tracking
+`jupyterhub_<noun>_<verb>_<type_suffix>`. So a histogram that's tracking
 the duration (in seconds) of servers spawning would be called
-SERVER_SPAWN_DURATION_SECONDS.
+jupyterhub_server_spawn_duration_seconds.

 We also create an Enum for each 'status' type label in every metric
 we collect. This is to make sure that the metrics exist regardless
@@ -14,6 +14,10 @@ create them, the metric spawn_duration_seconds{status="failure"}
 will not actually exist until the first failure. This makes dashboarding
 and alerting difficult, so we explicitly list statuses and create
 them manually here.
+
+.. versionchanged:: 1.3
+
+    added ``jupyterhub_`` prefix to metric names.
 """
 from enum import Enum

@@ -21,13 +25,13 @@ from prometheus_client import Gauge
 from prometheus_client import Histogram

 REQUEST_DURATION_SECONDS = Histogram(
-    'request_duration_seconds',
+    'jupyterhub_request_duration_seconds',
    'request duration for all HTTP requests',
    ['method', 'handler', 'code'],
 )

 SERVER_SPAWN_DURATION_SECONDS = Histogram(
-    'server_spawn_duration_seconds',
+    'jupyterhub_server_spawn_duration_seconds',
    'time taken for server spawning operation',
    ['status'],
    # Use custom bucket sizes, since the default bucket ranges
@@ -36,25 +40,27 @@ SERVER_SPAWN_DURATION_SECONDS = Histogram(
 )

 RUNNING_SERVERS = Gauge(
-    'running_servers', 'the number of user servers currently running'
+    'jupyterhub_running_servers', 'the number of user servers currently running'
 )

-TOTAL_USERS = Gauge('total_users', 'total number of users')
+TOTAL_USERS = Gauge('jupyterhub_total_users', 'total number of users')

 CHECK_ROUTES_DURATION_SECONDS = Histogram(
-    'check_routes_duration_seconds', 'Time taken to validate all routes in proxy'
+    'jupyterhub_check_routes_duration_seconds',
+    'Time taken to validate all routes in proxy',
 )

 HUB_STARTUP_DURATION_SECONDS = Histogram(
-    'hub_startup_duration_seconds', 'Time taken for Hub to start'
+    'jupyterhub_hub_startup_duration_seconds', 'Time taken for Hub to start'
 )

 INIT_SPAWNERS_DURATION_SECONDS = Histogram(
-    'init_spawners_duration_seconds', 'Time taken for spawners to initialize'
+    'jupyterhub_init_spawners_duration_seconds', 'Time taken for spawners to initialize'
 )

 PROXY_POLL_DURATION_SECONDS = Histogram(
-    'proxy_poll_duration_seconds', 'duration for polling all routes from proxy'
+    'jupyterhub_proxy_poll_duration_seconds',
+    'duration for polling all routes from proxy',
 )


@@ -79,7 +85,9 @@ for s in ServerSpawnStatus:


 PROXY_ADD_DURATION_SECONDS = Histogram(
-    'proxy_add_duration_seconds', 'duration for adding user routes to proxy', ['status']
+    'jupyterhub_proxy_add_duration_seconds',
+    'duration for adding user routes to proxy',
+    ['status'],
 )


@@ -100,7 +108,7 @@ for s in ProxyAddStatus:


 SERVER_POLL_DURATION_SECONDS = Histogram(
-    'server_poll_duration_seconds',
+    'jupyterhub_server_poll_duration_seconds',
    'time taken to poll if server is running',
    ['status'],
 )
@@ -127,7 +135,9 @@ for s in ServerPollStatus:


 SERVER_STOP_DURATION_SECONDS = Histogram(
-    'server_stop_seconds', 'time taken for server stopping operation', ['status']
+    'jupyterhub_server_stop_seconds',
+    'time taken for server stopping operation',
+    ['status'],
 )


@@ -148,7 +158,7 @@ for s in ServerStopStatus:


 PROXY_DELETE_DURATION_SECONDS = Histogram(
-    'proxy_delete_duration_seconds',
+    'jupyterhub_proxy_delete_duration_seconds',
    'duration for deleting user routes from proxy',
    ['status'],
 )
--- a/jupyterhub/oauth/provider.py
+++ b/jupyterhub/oauth/provider.py
@@ -256,7 +256,7 @@ class JupyterHubRequestValidator(RequestValidator):
        self.db.commit()

    def get_authorization_code_scopes(self, client_id, code, redirect_uri, request):
-        """ Extracts scopes from saved authorization code.
+        """Extracts scopes from saved authorization code.
        The scopes returned by this method is used to route token requests
        based on scopes passed to Authorization Code requests.
        With that the token endpoint knows when to include OpenIDConnect
--- a/jupyterhub/pagination.py
+++ b/jupyterhub/pagination.py
@@ -1,69 +1,93 @@
 """Basic class to manage pagination utils."""
 # Copyright (c) Jupyter Development Team.
 # Distributed under the terms of the Modified BSD License.
+from traitlets import default
+from traitlets import Integer
+from traitlets import observe
+from traitlets import Unicode
+from traitlets import validate
+from traitlets.config import Configurable


-class Pagination:
+class Pagination(Configurable):

-    _page_name = 'page'
-    _per_page_name = 'per_page'
-    _default_page = 1
-    _default_per_page = 100
-    _max_per_page = 250
+    # configurable options
+    default_per_page = Integer(
+        100,
+        config=True,
+        help="Default number of entries per page for paginated results.",
+    )

-    def __init__(self, *args, **kwargs):
-        """Potential parameters.
-        **url**: URL in request
-        **page**: current page in use
-        **per_page**: number of records to display in the page. By default 100
-        **total**: total records considered while paginating
-        """
-        self.page = kwargs.get(self._page_name, 1)
+    max_per_page = Integer(
+        250,
+        config=True,
+        help="Maximum number of entries per page for paginated results.",
+    )

-        if self.per_page > self._max_per_page:
-            self.per_page = self._max_per_page
+    # state variables
+    url = Unicode("")
+    page = Integer(1)
+    per_page = Integer(1, min=1)

-        self.total = int(kwargs.get('total', 0))
-        self.url = kwargs.get('url') or self.get_url()
-        self.init_values()
+    @default("per_page")
+    def _default_per_page(self):
+        return self.default_per_page

-    def init_values(self):
-        self._cached = {}
-        self.skip = (self.page - 1) * self.per_page
-        pages = divmod(self.total, self.per_page)
-        self.total_pages = pages[0] + 1 if pages[1] else pages[0]
+    @validate("per_page")
+    def _limit_per_page(self, proposal):
+        if self.max_per_page and proposal.value > self.max_per_page:
+            return self.max_per_page
+        if proposal.value <= 1:
+            return 1
+        return proposal.value

-        self.has_prev = self.page > 1
-        self.has_next = self.page < self.total_pages
+    @observe("max_per_page")
+    def _apply_max(self, change):
+        if change.new:
+            self.per_page = min(change.new, self.per_page)
+
+    total = Integer(0)
+
+    total_pages = Integer(0)
+
+    @default("total_pages")
+    def _calculate_total_pages(self):
+        total_pages = self.total // self.per_page
+        if self.total % self.per_page:
+            # there's a remainder, add 1
+            total_pages += 1
+        return total_pages
+
+    @observe("per_page", "total")
+    def _update_total_pages(self, change):
+        """Update total_pages when per_page or total is changed"""
+        self.total_pages = self._calculate_total_pages()
+
+    separator = Unicode("...")

-    @classmethod
    def get_page_args(self, handler):
        """
        This method gets the arguments used in the webpage to configurate the pagination
        In case of no arguments, it uses the default values from this class

-        It returns:
-          - self.page: The page requested for paginating or the default value (1)
-          - self.per_page: The number of items to return in this page. By default 100 and no more than 250
-          - self.per_page * (self.page - 1): The offset to consider when managing pagination via the ORM
+        Returns:
+          - page: The page requested for paginating or the default value (1)
+          - per_page: The number of items to return in this page. No more than max_per_page
+          - offset: The offset to consider when managing pagination via the ORM
        """
-        self.page = handler.get_argument(self._page_name, self._default_page)
-        self.per_page = handler.get_argument(
-            self._per_page_name, self._default_per_page
-        )
+        page = handler.get_argument("page", 1)
+        per_page = handler.get_argument("per_page", self.default_per_page)
        try:
-            self.per_page = int(self.per_page)
-            if self.per_page > self._max_per_page:
-                self.per_page = self._max_per_page
-        except:
-            self.per_page = self._default_per_page
+            self.per_page = int(per_page)
+        except Exception:
+            self.per_page = self.default_per_page

        try:
-            self.page = int(self.page)
+            self.page = int(page)
            if self.page < 1:
-                self.page = self._default_page
-        except:
-            self.page = self._default_page
+                self.page = 1
+        except Exception:
+            self.page = 1

        return self.page, self.per_page, self.per_page * (self.page - 1)

@@ -81,55 +105,61 @@ class Pagination:
        return {'total': self.total, 'start': start, 'end': end}

    def calculate_pages_window(self):
-        """Calculates the set of pages to render later in links() method. 
-           It returns the list of pages to render via links for the pagination 
-           By default, as we've observed in other applications, we're going to render
-           only a finite and predefined number of pages, avoiding visual fatigue related
-           to a long list of pages. By default, we render 7 pages plus some inactive links with the characters '...'
-           to point out that there are other pages that aren't explicitly rendered.
-           The primary way of work is to provide current webpage and 5 next pages, the last 2 ones 
-           (in case the current page + 5 does not overflow the total lenght of pages) and the first one for reference.
-           """
+        """Calculates the set of pages to render later in links() method.
+        It returns the list of pages to render via links for the pagination
+        By default, as we've observed in other applications, we're going to render
+        only a finite and predefined number of pages, avoiding visual fatigue related
+        to a long list of pages. By default, we render 7 pages plus some inactive links with the characters '...'
+        to point out that there are other pages that aren't explicitly rendered.
+        The primary way of work is to provide current webpage and 5 next pages, the last 2 ones
+        (in case the current page + 5 does not overflow the total lenght of pages) and the first one for reference.
+        """

-        self.separator_character = '...'
-        default_pages_to_render = 7
-        after_page = 5
-        before_end = 2
+        before_page = 2
+        after_page = 2
+        window_size = before_page + after_page + 1

-        # Add 1 to self.total_pages since our default page is 1 and not 0
-        total_pages = self.total_pages + 1
+        # Add 1 to total_pages since our starting page is 1 and not 0
+        last_page = self.total_pages

        pages = []

-        if total_pages > default_pages_to_render:
-            if self.page > 1:
-                pages.extend([1, '...'])
+        # will default window + start, end fit without truncation?
+        if self.total_pages > window_size + 2:
+            if self.page - before_page > 1:
+                # before_page will not reach page 1
+                pages.append(1)
+                if self.page - before_page > 2:
+                    # before_page will not reach page 2, need separator
+                    pages.append(self.separator)

-            if total_pages < self.page + after_page:
-                pages.extend(list(range(self.page, total_pages)))
+            pages.extend(range(max(1, self.page - before_page), self.page))
+            # we now have up to but not including self.page
+
+            if self.page + after_page + 1 >= last_page:
+                # after_page gets us to the end
+                pages.extend(range(self.page, last_page + 1))
            else:
-                if total_pages >= self.page + after_page + before_end:
-                    pages.extend(list(range(self.page, self.page + after_page)))
-                    pages.append('...')
-                    pages.extend(list(range(total_pages - before_end, total_pages)))
-                else:
-                    pages.extend(list(range(self.page, self.page + after_page)))
-                    if self.page + after_page < total_pages:
-                        # show only last page when the after_page window left space to show it
-                        pages.append('...')
-                        pages.extend(list(range(total_pages - 1, total_pages)))
+                # add full after_page entries
+                pages.extend(range(self.page, self.page + after_page + 1))
+                # add separator *if* this doesn't get to last page - 1
+                if self.page + after_page < last_page - 1:
+                    pages.append(self.separator)
+                pages.append(last_page)

            return pages

        else:
-            return list(range(1, total_pages))
+            # everything will fit, nothing to think about
+            # always return at least one page
+            return list(range(1, last_page + 1)) or [1]

    @property
    def links(self):
        """Get the links for the pagination.
-           Getting the input from calculate_pages_window(), generates the HTML code
-           for the pages to render, plus the arrows to go onwards and backwards (if needed).
-           """
+        Getting the input from calculate_pages_window(), generates the HTML code
+        for the pages to render, plus the arrows to go onwards and backwards (if needed).
+        """
        if self.total_pages == 1:
            return []

@@ -155,9 +185,11 @@ class Pagination:
                        page=page
                    )
                )
-            elif page == self.separator_character:
+            elif page == self.separator:
                links.append(
-                    '<li class="disabled"><span> <span aria-hidden="true">...</span></span></li>'
+                    '<li class="disabled"><span> <span aria-hidden="true">{separator}</span></span></li>'.format(
+                        separator=self.separator
+                    )
                )
            else:
                links.append(
--- a/jupyterhub/proxy.py
+++ b/jupyterhub/proxy.py
@@ -25,7 +25,6 @@ from functools import wraps
 from subprocess import Popen
 from urllib.parse import quote

-from tornado import gen
 from tornado.httpclient import AsyncHTTPClient
 from tornado.httpclient import HTTPError
 from tornado.httpclient import HTTPRequest
@@ -43,6 +42,7 @@ from . import utils
 from .metrics import CHECK_ROUTES_DURATION_SECONDS
 from .metrics import PROXY_POLL_DURATION_SECONDS
 from .objects import Server
+from .utils import exponential_backoff
 from .utils import make_ssl_context
 from .utils import url_path_join
 from jupyterhub.traitlets import Command
@@ -291,7 +291,7 @@ class Proxy(LoggingConfigurable):
            if service.server:
                futures.append(self.add_service(service))
        # wait after submitting them all
-        await gen.multi(futures)
+        await asyncio.gather(*futures)

    async def add_all_users(self, user_dict):
        """Update the proxy table from the database.
@@ -304,7 +304,7 @@ class Proxy(LoggingConfigurable):
                if spawner.ready:
                    futures.append(self.add_user(user, name))
        # wait after submitting them all
-        await gen.multi(futures)
+        await asyncio.gather(*futures)

    @_one_at_a_time
    async def check_routes(self, user_dict, service_dict, routes=None):
@@ -390,7 +390,7 @@ class Proxy(LoggingConfigurable):
                self.log.warning("Deleting stale route %s", routespec)
                futures.append(self.delete_route(routespec))

-        await gen.multi(futures)
+        await asyncio.gather(*futures)
        stop = time.perf_counter()  # timer stops here when user is deleted
        CHECK_ROUTES_DURATION_SECONDS.observe(stop - start)  # histogram metric

@@ -496,6 +496,19 @@ class ConfigurableHTTPProxy(Proxy):

            if not psutil.pid_exists(pid):
                raise ProcessLookupError
+
+            try:
+                process = psutil.Process(pid)
+                if self.command and self.command[0]:
+                    process_cmd = process.cmdline()
+                    if process_cmd and not any(
+                        self.command[0] in clause for clause in process_cmd
+                    ):
+                        raise ProcessLookupError
+            except (psutil.AccessDenied, psutil.NoSuchProcess):
+                # If there is a process at the proxy's PID but we don't have permissions to see it,
+                # then it is unlikely to actually be the proxy.
+                raise ProcessLookupError
        else:
            os.kill(pid, 0)

@@ -573,6 +586,34 @@ class ConfigurableHTTPProxy(Proxy):
            self.log.debug("PID file %s already removed", self.pid_file)
            pass

+    def _get_ssl_options(self):
+        """List of cmd proxy options to use internal SSL"""
+        cmd = []
+        proxy_api = 'proxy-api'
+        proxy_client = 'proxy-client'
+        api_key = self.app.internal_proxy_certs[proxy_api][
+            'keyfile'
+        ]  # Check content in next test and just patch manulaly or in the config of the file
+        api_cert = self.app.internal_proxy_certs[proxy_api]['certfile']
+        api_ca = self.app.internal_trust_bundles[proxy_api + '-ca']
+
+        client_key = self.app.internal_proxy_certs[proxy_client]['keyfile']
+        client_cert = self.app.internal_proxy_certs[proxy_client]['certfile']
+        client_ca = self.app.internal_trust_bundles[proxy_client + '-ca']
+
+        cmd.extend(['--api-ssl-key', api_key])
+        cmd.extend(['--api-ssl-cert', api_cert])
+        cmd.extend(['--api-ssl-ca', api_ca])
+        cmd.extend(['--api-ssl-request-cert'])
+        cmd.extend(['--api-ssl-reject-unauthorized'])
+
+        cmd.extend(['--client-ssl-key', client_key])
+        cmd.extend(['--client-ssl-cert', client_cert])
+        cmd.extend(['--client-ssl-ca', client_ca])
+        cmd.extend(['--client-ssl-request-cert'])
+        cmd.extend(['--client-ssl-reject-unauthorized'])
+        return cmd
+
    async def start(self):
        """Start the proxy process"""
        # check if there is a previous instance still around
@@ -604,27 +645,7 @@ class ConfigurableHTTPProxy(Proxy):
        if self.ssl_cert:
            cmd.extend(['--ssl-cert', self.ssl_cert])
        if self.app.internal_ssl:
-            proxy_api = 'proxy-api'
-            proxy_client = 'proxy-client'
-            api_key = self.app.internal_proxy_certs[proxy_api]['keyfile']
-            api_cert = self.app.internal_proxy_certs[proxy_api]['certfile']
-            api_ca = self.app.internal_trust_bundles[proxy_api + '-ca']
-
-            client_key = self.app.internal_proxy_certs[proxy_client]['keyfile']
-            client_cert = self.app.internal_proxy_certs[proxy_client]['certfile']
-            client_ca = self.app.internal_trust_bundles[proxy_client + '-ca']
-
-            cmd.extend(['--api-ssl-key', api_key])
-            cmd.extend(['--api-ssl-cert', api_cert])
-            cmd.extend(['--api-ssl-ca', api_ca])
-            cmd.extend(['--api-ssl-request-cert'])
-            cmd.extend(['--api-ssl-reject-unauthorized'])
-
-            cmd.extend(['--client-ssl-key', client_key])
-            cmd.extend(['--client-ssl-cert', client_cert])
-            cmd.extend(['--client-ssl-ca', client_ca])
-            cmd.extend(['--client-ssl-request-cert'])
-            cmd.extend(['--client-ssl-reject-unauthorized'])
+            cmd.extend(self._get_ssl_options())
        if self.app.statsd_host:
            cmd.extend(
                [
@@ -691,8 +712,17 @@ class ConfigurableHTTPProxy(Proxy):
        parent = psutil.Process(pid)
        children = parent.children(recursive=True)
        for child in children:
-            child.kill()
-        psutil.wait_procs(children, timeout=5)
+            child.terminate()
+        gone, alive = psutil.wait_procs(children, timeout=5)
+        for p in alive:
+            p.kill()
+        # Clear the shell, too, if it still exists.
+        try:
+            parent.terminate()
+            parent.wait(timeout=5)
+            parent.kill()
+        except psutil.NoSuchProcess:
+            pass

    def _terminate(self):
        """Terminate our process"""
@@ -768,10 +798,36 @@ class ConfigurableHTTPProxy(Proxy):
            method=method,
            headers={'Authorization': 'token {}'.format(self.auth_token)},
            body=body,
+            connect_timeout=3,  # default: 20s
+            request_timeout=10,  # default: 20s
        )
-        async with self.semaphore:
-            result = await client.fetch(req)
-            return result
+
+        async def _wait_for_api_request():
+            try:
+                async with self.semaphore:
+                    return await client.fetch(req)
+            except HTTPError as e:
+                # Retry on potentially transient errors in CHP, typically
+                # numbered 500 and up. Note that CHP isn't able to emit 429
+                # errors.
+                if e.code >= 500:
+                    self.log.warning(
+                        "api_request to the proxy failed with status code {}, retrying...".format(
+                            e.code
+                        )
+                    )
+                    return False  # a falsy return value make exponential_backoff retry
+                else:
+                    self.log.error("api_request to proxy failed: {0}".format(e))
+                    # An unhandled error here will help the hub invoke cleanup logic
+                    raise
+
+        result = await exponential_backoff(
+            _wait_for_api_request,
+            'Repeated api_request to proxy path "{}" failed.'.format(path),
+            timeout=30,
+        )
+        return result

    async def add_route(self, routespec, target, data):
        body = data or {}
--- a/jupyterhub/services/auth.py
+++ b/jupyterhub/services/auth.py
@@ -23,7 +23,6 @@ from urllib.parse import quote
 from urllib.parse import urlencode

 import requests
-from tornado.gen import coroutine
 from tornado.httputil import url_concat
 from tornado.log import app_log
 from tornado.web import HTTPError
@@ -288,7 +287,7 @@ class HubAuth(SingletonConfigurable):

    def _check_hub_authorization(self, url, cache_key=None, use_cache=True):
        """Identify a user with the Hub
-        
+
        Args:
            url (str): The API URL to check the Hub for authorization
                       (e.g. http://127.0.0.1:8081/hub/api/authorizations/token/abc-def)
@@ -604,10 +603,10 @@ class HubOAuth(HubAuth):

    def token_for_code(self, code):
        """Get token for OAuth temporary code
-        
+
        This is the last step of OAuth login.
        Should be called in OAuth Callback handler.
-        
+
        Args:
            code (str): oauth code for finishing OAuth login
        Returns:
@@ -950,8 +949,7 @@ class HubOAuthCallbackHandler(HubOAuthenticated, RequestHandler):
    .. versionadded: 0.8
    """

-    @coroutine
-    def get(self):
+    async def get(self):
        error = self.get_argument("error", False)
        if error:
            msg = self.get_argument("error_description", error)
--- a/jupyterhub/singleuser/mixins.py
+++ b/jupyterhub/singleuser/mixins.py
@@ -20,7 +20,6 @@ from urllib.parse import urlparse

 from jinja2 import ChoiceLoader
 from jinja2 import FunctionLoader
-from tornado import gen
 from tornado import ioloop
 from tornado.httpclient import AsyncHTTPClient
 from tornado.httpclient import HTTPRequest
@@ -434,7 +433,7 @@ class SingleUserNotebookAppMixin(Configurable):
                    i,
                    RETRIES,
                )
-                await gen.sleep(min(2 ** i, 16))
+                await asyncio.sleep(min(2 ** i, 16))
            else:
                break
        else:
--- a/jupyterhub/spawner.py
+++ b/jupyterhub/spawner.py
@@ -16,8 +16,7 @@ from tempfile import mkdtemp

 if os.name == 'nt':
    import psutil
-from async_generator import async_generator
-from async_generator import yield_
+from async_generator import aclosing
 from sqlalchemy import inspect
 from tornado.ioloop import PeriodicCallback
 from traitlets import Any
@@ -354,8 +353,9 @@ class Spawner(LoggingConfigurable):

        return options_form

-    def options_from_form(self, form_data):
-        """Interpret HTTP form data
+    options_from_form = Callable(
+        help="""
+        Interpret HTTP form data

        Form data will always arrive as a dict of lists of strings.
        Override this function to understand single-values, numbers, etc.
@@ -379,7 +379,14 @@ class Spawner(LoggingConfigurable):
            (with additional support for bytes in case of uploaded file data),
            and any non-bytes non-jsonable values will be replaced with None
            if the user_options are re-used.
-        """
+        """,
+    ).tag(config=True)
+
+    @default("options_from_form")
+    def _options_from_form(self):
+        return self._default_options_from_form
+
+    def _default_options_from_form(self, form_data):
        return form_data

    def options_from_query(self, query_data):
@@ -1024,7 +1031,6 @@ class Spawner(LoggingConfigurable):
    def _progress_url(self):
        return self.user.progress_url(self.name)

-    @async_generator
    async def _generate_progress(self):
        """Private wrapper of progress generator

@@ -1036,21 +1042,17 @@ class Spawner(LoggingConfigurable):
            )
            return

-        await yield_({"progress": 0, "message": "Server requested"})
-        from async_generator import aclosing
+        yield {"progress": 0, "message": "Server requested"}

        async with aclosing(self.progress()) as progress:
            async for event in progress:
-                await yield_(event)
+                yield event

-    @async_generator
    async def progress(self):
        """Async generator for progress events

        Must be an async generator

-        For Python 3.5-compatibility, use the async_generator package
-
        Should yield messages of the form:

        ::
@@ -1067,7 +1069,7 @@ class Spawner(LoggingConfigurable):

        .. versionadded:: 0.9
        """
-        await yield_({"progress": 50, "message": "Spawning server..."})
+        yield {"progress": 50, "message": "Spawning server..."}

    async def start(self):
        """Start the single-user server
@@ -1078,9 +1080,7 @@ class Spawner(LoggingConfigurable):
        .. versionchanged:: 0.7
            Return ip, port instead of setting on self.user.server directly.
        """
-        raise NotImplementedError(
-            "Override in subclass. Must be a Tornado gen.coroutine."
-        )
+        raise NotImplementedError("Override in subclass. Must be a coroutine.")

    async def stop(self, now=False):
        """Stop the single-user server
@@ -1093,9 +1093,7 @@ class Spawner(LoggingConfigurable):

        Must be a coroutine.
        """
-        raise NotImplementedError(
-            "Override in subclass. Must be a Tornado gen.coroutine."
-        )
+        raise NotImplementedError("Override in subclass. Must be a coroutine.")

    async def poll(self):
        """Check if the single-user process is running
@@ -1121,9 +1119,7 @@ class Spawner(LoggingConfigurable):
          process has not yet completed.

        """
-        raise NotImplementedError(
-            "Override in subclass. Must be a Tornado gen.coroutine."
-        )
+        raise NotImplementedError("Override in subclass. Must be a coroutine.")

    def add_poll_callback(self, callback, *args, **kwargs):
        """Add a callback to fire when the single-user server stops"""
--- a/jupyterhub/tests/conftest.py
+++ b/jupyterhub/tests/conftest.py
@@ -36,7 +36,6 @@ from unittest import mock

 from pytest import fixture
 from pytest import raises
-from tornado import gen
 from tornado import ioloop
 from tornado.httpclient import HTTPError
 from tornado.platform.asyncio import AsyncIOMainLoop
@@ -56,13 +55,16 @@ _db = None


 def pytest_collection_modifyitems(items):
-    """add asyncio marker to all async tests"""
+    """This function is automatically run by pytest passing all collected test
+    functions.
+
+    We use it to add asyncio marker to all async tests and assert we don't use
+    test functions that are async generators which wouldn't make sense.
+    """
    for item in items:
        if inspect.iscoroutinefunction(item.obj):
            item.add_marker('asyncio')
-        if hasattr(inspect, 'isasyncgenfunction'):
-            # double-check that we aren't mixing yield and async def
-            assert not inspect.isasyncgenfunction(item.obj)
+        assert not inspect.isasyncgenfunction(item.obj)


@fixture(scope='module')
@@ -74,7 +76,9 @@ def ssl_tmpdir(tmpdir_factory):
 def app(request, io_loop, ssl_tmpdir):
    """Mock a jupyterhub app for testing"""
    mocked_app = None
-    ssl_enabled = getattr(request.module, "ssl_enabled", False)
+    ssl_enabled = getattr(
+        request.module, 'ssl_enabled', os.environ.get('SSL_ENABLED', False)
+    )
    kwargs = dict()
    if ssl_enabled:
        kwargs.update(dict(internal_ssl=True, internal_certs_location=str(ssl_tmpdir)))
@@ -214,7 +218,7 @@ def admin_user(app, username):
 class MockServiceSpawner(jupyterhub.services.service._ServiceSpawner):
    """mock services for testing.

-       Shorter intervals, etc.
+    Shorter intervals, etc.
    """

    poll_interval = 1
@@ -244,17 +248,14 @@ def _mockservice(request, app, url=False):
        assert name in app._service_map
        service = app._service_map[name]

-        @gen.coroutine
-        def start():
+        async def start():
            # wait for proxy to be updated before starting the service
-            yield app.proxy.add_all_services(app._service_map)
+            await app.proxy.add_all_services(app._service_map)
            service.start()

        io_loop.run_sync(start)

        def cleanup():
-            import asyncio
-
            asyncio.get_event_loop().run_until_complete(service.stop())
            app.services[:] = []
            app._service_map.clear()
--- a/jupyterhub/tests/mocking.py
+++ b/jupyterhub/tests/mocking.py
@@ -36,13 +36,12 @@ from unittest import mock
 from urllib.parse import urlparse

 from pamela import PAMError
-from tornado import gen
-from tornado.concurrent import Future
 from tornado.ioloop import IOLoop
 from traitlets import Bool
 from traitlets import default
 from traitlets import Dict

+from .. import metrics
 from .. import orm
 from ..app import JupyterHub
 from ..auth import PAMAuthenticator
@@ -110,19 +109,17 @@ class SlowSpawner(MockSpawner):
    delay = 2
    _start_future = None

-    @gen.coroutine
-    def start(self):
-        (ip, port) = yield super().start()
+    async def start(self):
+        (ip, port) = await super().start()
        if self._start_future is not None:
-            yield self._start_future
+            await self._start_future
        else:
-            yield gen.sleep(self.delay)
+            await asyncio.sleep(self.delay)
        return ip, port

-    @gen.coroutine
-    def stop(self):
-        yield gen.sleep(self.delay)
-        yield super().stop()
+    async def stop(self):
+        await asyncio.sleep(self.delay)
+        await super().stop()


 class NeverSpawner(MockSpawner):
@@ -134,14 +131,12 @@ class NeverSpawner(MockSpawner):

    def start(self):
        """Return a Future that will never finish"""
-        return Future()
+        return asyncio.Future()

-    @gen.coroutine
-    def stop(self):
+    async def stop(self):
        pass

-    @gen.coroutine
-    def poll(self):
+    async def poll(self):
        return 0


@@ -215,8 +210,7 @@ class MockPAMAuthenticator(PAMAuthenticator):
        # skip the add-system-user bit
        return not user.name.startswith('dne')

-    @gen.coroutine
-    def authenticate(self, *args, **kwargs):
+    async def authenticate(self, *args, **kwargs):
        with mock.patch.multiple(
            'pamela',
            authenticate=mock_authenticate,
@@ -224,7 +218,7 @@ class MockPAMAuthenticator(PAMAuthenticator):
            close_session=mock_open_session,
            check_account=mock_check_account,
        ):
-            username = yield super(MockPAMAuthenticator, self).authenticate(
+            username = await super(MockPAMAuthenticator, self).authenticate(
                *args, **kwargs
            )
        if username is None:
@@ -320,14 +314,13 @@ class MockHub(JupyterHub):
                self.db.delete(group)
            self.db.commit()

-    @gen.coroutine
-    def initialize(self, argv=None):
+    async def initialize(self, argv=None):
        self.pid_file = NamedTemporaryFile(delete=False).name
        self.db_file = NamedTemporaryFile()
        self.db_url = os.getenv('JUPYTERHUB_TEST_DB_URL') or self.db_file.name
        if 'mysql' in self.db_url:
            self.db_kwargs['connect_args'] = {'auth_plugin': 'mysql_native_password'}
-        yield super().initialize([])
+        await super().initialize([])

        # add an initial user
        user = self.db.query(orm.User).filter(orm.User.name == 'user').first()
@@ -335,6 +328,7 @@ class MockHub(JupyterHub):
            user = orm.User(name='user')
            self.db.add(user)
            self.db.commit()
+            metrics.TOTAL_USERS.inc()

    def stop(self):
        super().stop()
@@ -358,14 +352,13 @@ class MockHub(JupyterHub):
        self.cleanup = lambda: None
        self.db_file.close()

-    @gen.coroutine
-    def login_user(self, name):
+    async def login_user(self, name):
        """Login a user by name, returning her cookies."""
        base_url = public_url(self)
        external_ca = None
        if self.internal_ssl:
            external_ca = self.external_certs['files']['ca']
-        r = yield async_requests.post(
+        r = await async_requests.post(
            base_url + 'hub/login',
            data={'username': name, 'password': name},
            allow_redirects=False,
@@ -407,8 +400,7 @@ class StubSingleUserSpawner(MockSpawner):

    _thread = None

-    @gen.coroutine
-    def start(self):
+    async def start(self):
        ip = self.ip = '127.0.0.1'
        port = self.port = random_port()
        env = self.get_env()
@@ -435,14 +427,12 @@ class StubSingleUserSpawner(MockSpawner):
        assert ready
        return (ip, port)

-    @gen.coroutine
-    def stop(self):
+    async def stop(self):
        self._app.stop()
        self._thread.join(timeout=30)
        assert not self._thread.is_alive()

-    @gen.coroutine
-    def poll(self):
+    async def poll(self):
        if self._thread is None:
            return 0
        if self._thread.is_alive():
--- a/jupyterhub/tests/mockservice.py
+++ b/jupyterhub/tests/mockservice.py
@@ -60,7 +60,7 @@ class APIHandler(web.RequestHandler):

 class WhoAmIHandler(HubAuthenticated, web.RequestHandler):
    """Reply with the name of the user who made the request.
-    
+
    Uses "deprecated" cookie login
    """

@@ -71,7 +71,7 @@ class WhoAmIHandler(HubAuthenticated, web.RequestHandler):

 class OWhoAmIHandler(HubOAuthenticated, web.RequestHandler):
    """Reply with the name of the user who made the request.
-    
+
    Uses OAuth login flow
    """

--- a/jupyterhub/tests/test_api.py
+++ b/jupyterhub/tests/test_api.py
@@ -1,22 +1,20 @@
 """Tests for the REST API."""
+import asyncio
 import json
 import re
 import sys
 import uuid
-from concurrent.futures import Future
 from datetime import datetime
 from datetime import timedelta
 from unittest import mock
 from urllib.parse import quote
 from urllib.parse import urlparse

-from async_generator import async_generator
-from async_generator import yield_
 from pytest import mark
-from tornado import gen

 import jupyterhub
 from .. import orm
+from ..objects import Server
 from ..utils import url_path_join as ujoin
 from ..utils import utcnow
 from .mocking import public_host
@@ -27,7 +25,6 @@ from .utils import async_requests
 from .utils import auth_header
 from .utils import find_user

-
 # --------------------
 # Authentication tests
 # --------------------
@@ -182,6 +179,71 @@ async def test_get_users(app):
    assert r.status_code == 403


+@mark.user
+@mark.parametrize(
+    "state",
+    ("inactive", "active", "ready", "invalid"),
+)
+async def test_get_users_state_filter(app, state):
+    db = app.db
+
+    # has_one_active: one active, one inactive, zero ready
+    has_one_active = add_user(db, app=app, name='has_one_active')
+    # has_two_active: two active, ready servers
+    has_two_active = add_user(db, app=app, name='has_two_active')
+    # has_two_inactive: two spawners, neither active
+    has_two_inactive = add_user(db, app=app, name='has_two_inactive')
+    # has_zero: no Spawners registered at all
+    has_zero = add_user(db, app=app, name='has_zero')
+
+    test_usernames = set(
+        ("has_one_active", "has_two_active", "has_two_inactive", "has_zero")
+    )
+
+    user_states = {
+        "inactive": ["has_two_inactive", "has_zero"],
+        "ready": ["has_two_active"],
+        "active": ["has_one_active", "has_two_active"],
+        "invalid": [],
+    }
+    expected = user_states[state]
+
+    def add_spawner(user, name='', active=True, ready=True):
+        """Add a spawner in a requested state
+
+        If active, should turn up in an active query
+        If active and ready, should turn up in a ready query
+        If not active, should turn up in an inactive query
+        """
+        spawner = user.spawners[name]
+        db.commit()
+        if active:
+            orm_server = orm.Server()
+            db.add(orm_server)
+            db.commit()
+            spawner.server = Server(orm_server=orm_server)
+            db.commit()
+            if not ready:
+                spawner._spawn_pending = True
+        return spawner
+
+    for name in ("", "secondary"):
+        add_spawner(has_two_active, name, active=True)
+        add_spawner(has_two_inactive, name, active=False)
+
+    add_spawner(has_one_active, active=True, ready=False)
+    add_spawner(has_one_active, "inactive", active=False)
+
+    r = await api_request(app, 'users?state={}'.format(state))
+    if state == "invalid":
+        assert r.status_code == 400
+        return
+    assert r.status_code == 200
+
+    usernames = sorted(u["name"] for u in r.json() if u["name"] in test_usernames)
+    assert usernames == expected
+
+
@mark.user
 async def test_get_self(app):
    db = app.db
@@ -215,6 +277,17 @@ async def test_get_self(app):
    assert r.status_code == 403


+async def test_get_self_service(app, mockservice):
+    r = await api_request(
+        app, "user", headers={"Authorization": f"token {mockservice.api_token}"}
+    )
+    r.raise_for_status()
+    service_info = r.json()
+
+    assert service_info['kind'] == 'service'
+    assert service_info['name'] == mockservice.name
+
+
@mark.user
 async def test_add_user(app):
    db = app.db
@@ -613,7 +686,7 @@ async def test_slow_spawn(app, no_patience, slow_spawn):

    async def wait_spawn():
        while not app_user.running:
-            await gen.sleep(0.1)
+            await asyncio.sleep(0.1)

    await wait_spawn()
    assert not app_user.spawner._spawn_pending
@@ -622,7 +695,7 @@ async def test_slow_spawn(app, no_patience, slow_spawn):

    async def wait_stop():
        while app_user.spawner._stop_pending:
-            await gen.sleep(0.1)
+            await asyncio.sleep(0.1)

    r = await api_request(app, 'users', name, 'server', method='delete')
    r.raise_for_status()
@@ -656,7 +729,7 @@ async def test_never_spawn(app, no_patience, never_spawn):
    assert app.users.count_active_users()['pending'] == 1

    while app_user.spawner.pending:
-        await gen.sleep(0.1)
+        await asyncio.sleep(0.1)
        print(app_user.spawner.pending)

    assert not app_user.spawner._spawn_pending
@@ -682,7 +755,7 @@ async def test_slow_bad_spawn(app, no_patience, slow_bad_spawn):
    r = await api_request(app, 'users', name, 'server', method='post')
    r.raise_for_status()
    while user.spawner.pending:
-        await gen.sleep(0.1)
+        await asyncio.sleep(0.1)
    # spawn failed
    assert not user.running
    assert app.users.count_active_users()['pending'] == 0
@@ -818,32 +891,12 @@ async def test_progress_bad_slow(request, app, no_patience, slow_bad_spawn):
    }


-@async_generator
 async def progress_forever():
    """progress function that yields messages forever"""
    for i in range(1, 10):
-        await yield_({'progress': i, 'message': 'Stage %s' % i})
+        yield {'progress': i, 'message': 'Stage %s' % i}
        # wait a long time before the next event
-        await gen.sleep(10)
-
-
-if sys.version_info >= (3, 6):
-    # additional progress_forever defined as native
-    # async generator
-    # to test for issues with async_generator wrappers
-    exec(
-        """
-async def progress_forever_native():
-    for i in range(1, 10):
-        yield {
-            'progress': i,
-            'message': 'Stage %s' % i,
-        }
-        # wait a long time before the next event
-        await gen.sleep(10)
-""",
-        globals(),
-    )
+        await asyncio.sleep(10)


 async def test_spawn_progress_cutoff(request, app, no_patience, slow_spawn):
@@ -854,11 +907,7 @@ async def test_spawn_progress_cutoff(request, app, no_patience, slow_spawn):
    db = app.db
    name = 'geddy'
    app_user = add_user(db, app=app, name=name)
-    if sys.version_info >= (3, 6):
-        # Python >= 3.6, try native async generator
-        app_user.spawner.progress = globals()['progress_forever_native']
-    else:
-        app_user.spawner.progress = progress_forever
+    app_user.spawner.progress = progress_forever
    app_user.spawner.delay = 1

    r = await api_request(app, 'users', name, 'server', method='post')
@@ -885,8 +934,8 @@ async def test_spawn_limit(app, no_patience, slow_spawn, request):
    # start two pending spawns
    names = ['ykka', 'hjarka']
    users = [add_user(db, app=app, name=name) for name in names]
-    users[0].spawner._start_future = Future()
-    users[1].spawner._start_future = Future()
+    users[0].spawner._start_future = asyncio.Future()
+    users[1].spawner._start_future = asyncio.Future()
    for name in names:
        await api_request(app, 'users', name, 'server', method='post')
    assert app.users.count_active_users()['pending'] == 2
@@ -894,7 +943,7 @@ async def test_spawn_limit(app, no_patience, slow_spawn, request):
    # ykka and hjarka's spawns are both pending. Essun should fail with 429
    name = 'essun'
    user = add_user(db, app=app, name=name)
-    user.spawner._start_future = Future()
+    user.spawner._start_future = asyncio.Future()
    r = await api_request(app, 'users', name, 'server', method='post')
    assert r.status_code == 429

@@ -902,7 +951,7 @@ async def test_spawn_limit(app, no_patience, slow_spawn, request):
    users[0].spawner._start_future.set_result(None)
    # wait for ykka to finish
    while not users[0].running:
-        await gen.sleep(0.1)
+        await asyncio.sleep(0.1)

    assert app.users.count_active_users()['pending'] == 1
    r = await api_request(app, 'users', name, 'server', method='post')
@@ -913,7 +962,7 @@ async def test_spawn_limit(app, no_patience, slow_spawn, request):
    for user in users[1:]:
        user.spawner._start_future.set_result(None)
    while not all(u.running for u in users):
-        await gen.sleep(0.1)
+        await asyncio.sleep(0.1)

    # everybody's running, pending count should be back to 0
    assert app.users.count_active_users()['pending'] == 0
@@ -922,7 +971,7 @@ async def test_spawn_limit(app, no_patience, slow_spawn, request):
        r = await api_request(app, 'users', u.name, 'server', method='delete')
        r.raise_for_status()
    while any(u.spawner.active for u in users):
-        await gen.sleep(0.1)
+        await asyncio.sleep(0.1)


@mark.slow
@@ -1000,7 +1049,7 @@ async def test_start_stop_race(app, no_patience, slow_spawn):
    r = await api_request(app, 'users', user.name, 'server', method='delete')
    assert r.status_code == 400
    while not spawner.ready:
-        await gen.sleep(0.1)
+        await asyncio.sleep(0.1)

    spawner.delay = 3
    # stop the spawner
@@ -1008,7 +1057,7 @@ async def test_start_stop_race(app, no_patience, slow_spawn):
    assert r.status_code == 202
    assert spawner.pending == 'stop'
    # make sure we get past deleting from the proxy
-    await gen.sleep(1)
+    await asyncio.sleep(1)
    # additional stops while stopping shouldn't trigger a new stop
    with mock.patch.object(spawner, 'stop') as m:
        r = await api_request(app, 'users', user.name, 'server', method='delete')
@@ -1020,7 +1069,7 @@ async def test_start_stop_race(app, no_patience, slow_spawn):
    assert r.status_code == 400

    while spawner.active:
-        await gen.sleep(0.1)
+        await asyncio.sleep(0.1)
    # start after stop is okay
    r = await api_request(app, 'users', user.name, 'server', method='post')
    assert r.status_code == 202
--- a/jupyterhub/tests/test_internal_ssl_api.py
+++ b/jupyterhub/tests/test_internal_ssl_api.py
@@ -1,6 +0,0 @@
-"""Tests for the SSL enabled REST API."""
-# Copyright (c) Jupyter Development Team.
-# Distributed under the terms of the Modified BSD License.
-from jupyterhub.tests.test_api import *
-
-ssl_enabled = True
--- a/jupyterhub/tests/test_internal_ssl_app.py
+++ b/jupyterhub/tests/test_internal_ssl_app.py
@@ -1,7 +0,0 @@
-"""Test the JupyterHub entry point with internal ssl"""
-# Copyright (c) Jupyter Development Team.
-# Distributed under the terms of the Modified BSD License.
-import jupyterhub.tests.mocking
-from jupyterhub.tests.test_app import *
-
-ssl_enabled = True
--- a/jupyterhub/tests/test_internal_ssl_connections.py
+++ b/jupyterhub/tests/test_internal_ssl_connections.py
@@ -20,8 +20,7 @@ ssl_enabled = True
 SSL_ERROR = (SSLError, ConnectionError)


-@gen.coroutine
-def wait_for_spawner(spawner, timeout=10):
+async def wait_for_spawner(spawner, timeout=10):
    """Wait for an http server to show up

    polling at shorter intervals for early termination
@@ -32,15 +31,15 @@ def wait_for_spawner(spawner, timeout=10):
        return spawner.server.wait_up(timeout=1, http=True)

    while time.monotonic() < deadline:
-        status = yield spawner.poll()
+        status = await spawner.poll()
        assert status is None
        try:
-            yield wait()
+            await wait()
        except TimeoutError:
            continue
        else:
            break
-    yield wait()
+    await wait()


 async def test_connection_hub_wrong_certs(app):
--- a/jupyterhub/tests/test_internal_ssl_spawner.py
+++ b/jupyterhub/tests/test_internal_ssl_spawner.py
@@ -1,6 +0,0 @@
-"""Tests for process spawning with internal_ssl"""
-# Copyright (c) Jupyter Development Team.
-# Distributed under the terms of the Modified BSD License.
-from jupyterhub.tests.test_spawner import *
-
-ssl_enabled = True
--- a/jupyterhub/tests/test_metrics.py
+++ b/jupyterhub/tests/test_metrics.py
@@ -0,0 +1,34 @@
+import json
+
+from .utils import add_user
+from .utils import api_request
+from jupyterhub import metrics
+from jupyterhub import orm
+
+
+async def test_total_users(app):
+    num_users = app.db.query(orm.User).count()
+    sample = metrics.TOTAL_USERS.collect()[0].samples[0]
+    assert sample.value == num_users
+
+    await api_request(
+        app, "/users", method="post", data=json.dumps({"usernames": ["incrementor"]})
+    )
+
+    sample = metrics.TOTAL_USERS.collect()[0].samples[0]
+    assert sample.value == num_users + 1
+
+    # GET /users used to double-count
+    await api_request(app, "/users")
+
+    # populate the Users cache dict if any are missing:
+    for user in app.db.query(orm.User):
+        _ = app.users[user.id]
+
+    sample = metrics.TOTAL_USERS.collect()[0].samples[0]
+    assert sample.value == num_users + 1
+
+    await api_request(app, "/users/incrementor", method="delete")
+
+    sample = metrics.TOTAL_USERS.collect()[0].samples[0]
+    assert sample.value == num_users
--- a/jupyterhub/tests/test_orm.py
+++ b/jupyterhub/tests/test_orm.py
@@ -222,8 +222,7 @@ async def test_spawn_fails(db):
    db.commit()

    class BadSpawner(MockSpawner):
-        @gen.coroutine
-        def start(self):
+        async def start(self):
            raise RuntimeError("Split the party")

    user = User(
--- a/jupyterhub/tests/test_pages.py
+++ b/jupyterhub/tests/test_pages.py
@@ -8,7 +8,6 @@ from urllib.parse import urlparse

 import pytest
 from bs4 import BeautifulSoup
-from tornado import gen
 from tornado.escape import url_escape
 from tornado.httputil import url_concat

@@ -31,7 +30,7 @@ async def test_root_no_auth(app):
    url = ujoin(public_host(app), app.hub.base_url)
    r = await async_requests.get(url)
    r.raise_for_status()
-    assert r.url == ujoin(url, 'login')
+    assert r.url == url_concat(ujoin(url, 'login'), dict(next=app.hub.base_url))


 async def test_root_auth(app):
@@ -266,7 +265,8 @@ async def test_spawn_with_query_arguments(app):
        next_url = ujoin(app.base_url, 'user/jones/tree')
        r = await async_requests.get(
            url_concat(
-                ujoin(base_url, 'spawn'), {'next': next_url, 'energy': '510keV'},
+                ujoin(base_url, 'spawn'),
+                {'next': next_url, 'energy': '510keV'},
            ),
            cookies=cookies,
        )
@@ -332,6 +332,12 @@ async def test_spawn_form_admin_access(app, admin_access):
            data={'bounds': ['-3', '3'], 'energy': '938MeV'},
        )
        r.raise_for_status()
+
+        while '/spawn-pending/' in r.url:
+            await asyncio.sleep(0.1)
+            r = await async_requests.get(r.url, cookies=cookies)
+            r.raise_for_status()
+
        assert r.history
        assert r.url.startswith(public_url(app, u))
        assert u.spawner.user_options == {
@@ -586,8 +592,7 @@ async def test_login_strip(app):
    base_url = public_url(app)
    called_with = []

-    @gen.coroutine
-    def mock_authenticate(handler, data):
+    async def mock_authenticate(handler, data):
        called_with.append(data)

    with mock.patch.object(app.authenticator, 'authenticate', mock_authenticate):
@@ -616,9 +621,16 @@ async def test_login_strip(app):
        (False, '//other.domain', '', None),
        (False, '///other.domain/triple', '', None),
        (False, '\\\\other.domain/backslashes', '', None),
-        # params are handled correctly
-        (True, '/hub/admin', 'hub/admin?left=1&right=2', [('left', 1), ('right', 2)]),
-        (False, '/hub/admin', 'hub/admin?left=1&right=2', [('left', 1), ('right', 2)]),
+        # params are handled correctly (ignored if ?next= specified)
+        (
+            True,
+            '/hub/admin?left=1&right=2',
+            'hub/admin?left=1&right=2',
+            {"left": "abc"},
+        ),
+        (False, '/hub/admin', 'hub/admin', [('left', 1), ('right', 2)]),
+        (True, '', '', {"keep": "yes"}),
+        (False, '', '', {"keep": "yes"}),
    ],
 )
 async def test_login_redirect(app, running, next_url, location, params):
@@ -627,10 +639,15 @@ async def test_login_redirect(app, running, next_url, location, params):
    if location:
        location = ujoin(app.base_url, location)
    elif running:
+        # location not specified,
        location = user.url
+        if params:
+            location = url_concat(location, params)
    else:
        # use default url
        location = ujoin(app.base_url, 'hub/spawn')
+        if params:
+            location = url_concat(location, params)

    url = 'login'
    if params:
@@ -649,7 +666,73 @@ async def test_login_redirect(app, running, next_url, location, params):
    r = await get_page(url, app, cookies=cookies, allow_redirects=False)
    r.raise_for_status()
    assert r.status_code == 302
-    assert location == r.headers['Location']
+    assert r.headers["Location"] == location
+
+
+@pytest.mark.parametrize(
+    'location, next, extra_params',
+    [
+        (
+            "{base_url}hub/spawn?a=5",
+            None,
+            {"a": "5"},
+        ),  # no ?next= given, preserve params
+        ("/x", "/x", {"a": "5"}),  # ?next=given, params ignored
+        (
+            "/x?b=10",
+            "/x?b=10",
+            {"a": "5"},
+        ),  # ?next=given with params, additional params ignored
+    ],
+)
+async def test_next_url(app, user, location, next, extra_params):
+    params = {}
+    if extra_params:
+        params.update(extra_params)
+    if next:
+        params["next"] = next
+    url = url_concat("/", params)
+    cookies = await app.login_user("monster")
+
+    # location can be a string template
+    location = location.format(base_url=app.base_url)
+
+    r = await get_page(url, app, cookies=cookies, allow_redirects=False)
+    r.raise_for_status()
+    assert r.status_code == 302
+    assert r.headers["Location"] == location
+
+
+async def test_next_url_params_sequence(app, user):
+    """Test each step of / -> login -> spawn
+
+    and whether they preserve url params
+    """
+    params = {"xyz": "5"}
+    # first request: root page, with params, not logged in
+    r = await get_page("/?xyz=5", app, allow_redirects=False)
+    r.raise_for_status()
+    location = r.headers["Location"]
+
+    # next page: login
+    cookies = await app.login_user(user.name)
+    assert location == url_concat(
+        ujoin(app.base_url, "/hub/login"), {"next": ujoin(app.base_url, "/hub/?xyz=5")}
+    )
+    r = await async_requests.get(
+        public_host(app) + location, cookies=cookies, allow_redirects=False
+    )
+    r.raise_for_status()
+    location = r.headers["Location"]
+
+    # after login, redirect back
+    assert location == ujoin(app.base_url, "/hub/?xyz=5")
+    r = await async_requests.get(
+        public_host(app) + location, cookies=cookies, allow_redirects=False
+    )
+    r.raise_for_status()
+    location = r.headers["Location"]
+    assert location == ujoin(app.base_url, "/hub/spawn?xyz=5")


 async def test_auto_login(app, request):
@@ -663,14 +746,18 @@ async def test_auto_login(app, request):
    )
    # no auto_login: end up at /hub/login
    r = await async_requests.get(base_url)
-    assert r.url == public_url(app, path='hub/login')
+    assert r.url == url_concat(
+        public_url(app, path="hub/login"), {"next": app.hub.base_url}
+    )
    # enable auto_login: redirect from /hub/login to /hub/dummy
    authenticator = Authenticator(auto_login=True)
    authenticator.login_url = lambda base_url: ujoin(base_url, 'dummy')

    with mock.patch.dict(app.tornado_settings, {'authenticator': authenticator}):
        r = await async_requests.get(base_url)
-    assert r.url == public_url(app, path='hub/dummy')
+    assert r.url == url_concat(
+        public_url(app, path="hub/dummy"), {"next": app.hub.base_url}
+    )


 async def test_auto_login_logout(app):
@@ -943,8 +1030,7 @@ async def test_pre_spawn_start_exc_no_form(app):
    exc = "pre_spawn_start error"

    # throw exception from pre_spawn_start
-    @gen.coroutine
-    def mock_pre_spawn_start(user, spawner):
+    async def mock_pre_spawn_start(user, spawner):
        raise Exception(exc)

    with mock.patch.object(app.authenticator, 'pre_spawn_start', mock_pre_spawn_start):
@@ -959,8 +1045,7 @@ async def test_pre_spawn_start_exc_options_form(app):
    exc = "pre_spawn_start error"

    # throw exception from pre_spawn_start
-    @gen.coroutine
-    def mock_pre_spawn_start(user, spawner):
+    async def mock_pre_spawn_start(user, spawner):
        raise Exception(exc)

    with mock.patch.dict(
--- a/jupyterhub/tests/test_pagination.py
+++ b/jupyterhub/tests/test_pagination.py
@@ -0,0 +1,52 @@
+"""tests for pagination"""
+from pytest import mark
+from pytest import raises
+from traitlets.config import Config
+
+from jupyterhub.pagination import Pagination
+
+
+@mark.parametrize(
+    "per_page, max_per_page, expected",
+    [
+        (20, 10, 10),
+        (1000, 1000, 1000),
+    ],
+)
+def test_per_page_bounds(per_page, max_per_page, expected):
+    cfg = Config()
+    cfg.Pagination.max_per_page = max_per_page
+    p = Pagination(config=cfg)
+    p.per_page = per_page
+    p.total = 99999
+    assert p.per_page == expected
+    with raises(Exception):
+        p.per_page = 0
+
+
+@mark.parametrize(
+    "page, per_page, total, expected",
+    [
+        (1, 10, 99, [1, 2, 3, "...", 10]),
+        (2, 10, 99, [1, 2, 3, 4, "...", 10]),
+        (3, 10, 99, [1, 2, 3, 4, 5, "...", 10]),
+        (4, 10, 99, [1, 2, 3, 4, 5, 6, "...", 10]),
+        (5, 10, 99, [1, "...", 3, 4, 5, 6, 7, "...", 10]),
+        (6, 10, 99, [1, "...", 4, 5, 6, 7, 8, "...", 10]),
+        (7, 10, 99, [1, "...", 5, 6, 7, 8, 9, 10]),
+        (8, 10, 99, [1, "...", 6, 7, 8, 9, 10]),
+        (9, 10, 99, [1, "...", 7, 8, 9, 10]),
+        (1, 20, 99, [1, 2, 3, 4, 5]),
+        (1, 10, 0, [1]),
+        (1, 10, 1, [1]),
+        (1, 10, 10, [1]),
+        (1, 10, 11, [1, 2]),
+        (1, 10, 50, [1, 2, 3, 4, 5]),
+        (1, 10, 60, [1, 2, 3, 4, 5, 6]),
+        (1, 10, 70, [1, 2, 3, 4, 5, 6, 7]),
+        (1, 10, 80, [1, 2, 3, "...", 8]),
+    ],
+)
+def test_window(page, per_page, total, expected):
+    pagination = Pagination(page=page, per_page=per_page, total=total)
+    assert pagination.calculate_pages_window() == expected
--- a/jupyterhub/tests/test_proxy.py
+++ b/jupyterhub/tests/test_proxy.py
@@ -9,12 +9,12 @@ from urllib.parse import urlparse
 import pytest
 from traitlets.config import Config

-from .. import orm
 from ..utils import url_path_join as ujoin
 from ..utils import wait_for_http_server
 from .mocking import MockHub
 from .test_api import add_user
 from .test_api import api_request
+from .utils import skip_if_ssl


@pytest.fixture
@@ -27,6 +27,7 @@ def disable_check_routes(app):
        app.last_activity_callback.start()


+@skip_if_ssl
 async def test_external_proxy(request):
    auth_token = 'secret!'
    proxy_ip = '127.0.0.1'
--- a/jupyterhub/tests/test_services.py
+++ b/jupyterhub/tests/test_services.py
@@ -6,9 +6,7 @@ from binascii import hexlify
 from contextlib import contextmanager
 from subprocess import Popen

-from async_generator import async_generator
 from async_generator import asynccontextmanager
-from async_generator import yield_
 from tornado.ioloop import IOLoop

 from ..utils import maybe_future
@@ -17,6 +15,7 @@ from ..utils import url_path_join
 from ..utils import wait_for_http_server
 from .mocking import public_url
 from .utils import async_requests
+from .utils import skip_if_ssl

 mockservice_path = os.path.dirname(os.path.abspath(__file__))
 mockservice_py = os.path.join(mockservice_path, 'mockservice.py')
@@ -24,7 +23,6 @@ mockservice_cmd = [sys.executable, mockservice_py]


@asynccontextmanager
-@async_generator
 async def external_service(app, name='mockservice'):
    env = {
        'JUPYTERHUB_API_TOKEN': hexlify(os.urandom(5)),
@@ -35,7 +33,7 @@ async def external_service(app, name='mockservice'):
    proc = Popen(mockservice_cmd, env=env)
    try:
        await wait_for_http_server(env['JUPYTERHUB_SERVICE_URL'])
-        await yield_(env)
+        yield env
    finally:
        proc.terminate()

@@ -63,6 +61,7 @@ async def test_managed_service(mockservice):
    assert service.proc.poll() is None


+@skip_if_ssl
 async def test_proxy_service(app, mockservice_url):
    service = mockservice_url
    name = service.name
@@ -76,6 +75,7 @@ async def test_proxy_service(app, mockservice_url):
    assert r.text.endswith(path)


+@skip_if_ssl
 async def test_external_service(app):
    name = 'external'
    async with external_service(app, name=name) as env:
--- a/jupyterhub/tests/test_services_auth.py
+++ b/jupyterhub/tests/test_services_auth.py
@@ -35,6 +35,7 @@ from .utils import AsyncSession

 # mock for sending monotonic counter way into the future
 monotonic_future = mock.patch('time.monotonic', lambda: sys.maxsize)
+ssl_enabled = False


 def test_expiring_dict():
--- a/jupyterhub/tests/test_spawner.py
+++ b/jupyterhub/tests/test_spawner.py
@@ -1,6 +1,7 @@
 """Tests for process spawning"""
 # Copyright (c) Jupyter Development Team.
 # Distributed under the terms of the Modified BSD License.
+import asyncio
 import logging
 import os
 import signal
@@ -12,7 +13,6 @@ from unittest import mock
 from urllib.parse import urlparse

 import pytest
-from tornado import gen

 from .. import orm
 from .. import spawner as spawnermod
@@ -123,7 +123,7 @@ async def test_stop_spawner_sigint_fails(db):
    await spawner.start()

    # wait for the process to get to the while True: loop
-    await gen.sleep(1)
+    await asyncio.sleep(1)

    status = await spawner.poll()
    assert status is None
@@ -138,7 +138,7 @@ async def test_stop_spawner_stop_now(db):
    await spawner.start()

    # wait for the process to get to the while True: loop
-    await gen.sleep(1)
+    await asyncio.sleep(1)

    status = await spawner.poll()
    assert status is None
@@ -165,7 +165,7 @@ async def test_spawner_poll(db):
    spawner.start_polling()

    # wait for the process to get to the while True: loop
-    await gen.sleep(1)
+    await asyncio.sleep(1)
    status = await spawner.poll()
    assert status is None

@@ -173,12 +173,12 @@ async def test_spawner_poll(db):
    proc.terminate()
    for i in range(10):
        if proc.poll() is None:
-            await gen.sleep(1)
+            await asyncio.sleep(1)
        else:
            break
    assert proc.poll() is not None

-    await gen.sleep(2)
+    await asyncio.sleep(2)
    status = await spawner.poll()
    assert status is not None

@@ -258,8 +258,7 @@ async def test_shell_cmd(db, tmpdir, request):


 def test_inherit_overwrite():
-    """On 3.6+ we check things are overwritten at import time
-    """
+    """On 3.6+ we check things are overwritten at import time"""
    if sys.version_info >= (3, 6):
        with pytest.raises(NotImplementedError):

--- a/jupyterhub/tests/test_utils.py
+++ b/jupyterhub/tests/test_utils.py
@@ -1,21 +1,22 @@
 """Tests for utilities"""
 import asyncio
+import time
+from concurrent.futures import ThreadPoolExecutor

 import pytest
 from async_generator import aclosing
-from async_generator import async_generator
-from async_generator import yield_
+from tornado import gen
+from tornado.concurrent import run_on_executor

 from ..utils import iterate_until


-@async_generator
 async def yield_n(n, delay=0.01):
    """Yield n items with a delay between each"""
    for i in range(n):
        if delay:
            await asyncio.sleep(delay)
-        await yield_(i)
+        yield i


 def schedule_future(io_loop, *, delay, result=None):
@@ -50,13 +51,40 @@ async def test_iterate_until(io_loop, deadline, n, delay, expected):
 async def test_iterate_until_ready_after_deadline(io_loop):
    f = schedule_future(io_loop, delay=0)

-    @async_generator
    async def gen():
        for i in range(5):
-            await yield_(i)
+            yield i

    yielded = []
    async with aclosing(iterate_until(f, gen())) as items:
        async for item in items:
            yielded.append(item)
    assert yielded == list(range(5))
+
+
+@gen.coroutine
+def tornado_coroutine():
+    yield gen.sleep(0.05)
+    return "ok"
+
+
+class TornadoCompat:
+    def __init__(self):
+        self.executor = ThreadPoolExecutor(1)
+
+    @run_on_executor
+    def on_executor(self):
+        time.sleep(0.05)
+        return "executor"
+
+    @gen.coroutine
+    def tornado_coroutine(self):
+        yield gen.sleep(0.05)
+        return "gen.coroutine"
+
+
+async def test_tornado_coroutines():
+    t = TornadoCompat()
+    # verify that tornado gen and executor methods return awaitables
+    assert (await t.on_executor()) == "executor"
+    assert (await t.tornado_coroutine()) == "gen.coroutine"
--- a/jupyterhub/tests/utils.py
+++ b/jupyterhub/tests/utils.py
@@ -1,9 +1,12 @@
 import asyncio
+import os
 from concurrent.futures import ThreadPoolExecutor

+import pytest
 import requests
 from certipy import Certipy

+from jupyterhub import metrics
 from jupyterhub import orm
 from jupyterhub.objects import Server
 from jupyterhub.utils import url_path_join as ujoin
@@ -52,6 +55,12 @@ def ssl_setup(cert_dir, authority_name):
    return external_certs


+"""Skip tests that don't work under internal-ssl when testing under internal-ssl"""
+skip_if_ssl = pytest.mark.skipif(
+    os.environ.get('SSL_ENABLED', False), reason="Does not use internal SSL"
+)
+
+
 def check_db_locks(func):
    """Decorator that verifies no locks are held on database upon exit.

@@ -97,6 +106,7 @@ def add_user(db, app=None, **kwargs):
    if orm_user is None:
        orm_user = orm.User(**kwargs)
        db.add(orm_user)
+        metrics.TOTAL_USERS.inc()
    else:
        for attr, value in kwargs.items():
            setattr(orm_user, attr, value)
--- a/jupyterhub/user.py
+++ b/jupyterhub/user.py
@@ -69,7 +69,6 @@ class UserDict(dict):
        """Add a user to the UserDict"""
        if orm_user.id not in self:
            self[orm_user.id] = self.from_orm(orm_user)
-            TOTAL_USERS.inc()
        return self[orm_user.id]

    def __contains__(self, key):
--- a/jupyterhub/utils.py
+++ b/jupyterhub/utils.py
@@ -21,10 +21,6 @@ from hmac import compare_digest
 from operator import itemgetter

 from async_generator import aclosing
-from async_generator import async_generator
-from async_generator import asynccontextmanager
-from async_generator import yield_
-from tornado import gen
 from tornado import ioloop
 from tornado import web
 from tornado.httpclient import AsyncHTTPClient
@@ -32,6 +28,15 @@ from tornado.httpclient import HTTPError
 from tornado.log import app_log
 from tornado.platform.asyncio import to_asyncio_future

+# For compatibility with python versions 3.6 or earlier.
+# asyncio.Task.all_tasks() is fully moved to asyncio.all_tasks() starting with 3.9. Also applies to current_task.
+try:
+    asyncio_all_tasks = asyncio.all_tasks
+    asyncio_current_task = asyncio.current_task
+except AttributeError as e:
+    asyncio_all_tasks = asyncio.Task.all_tasks
+    asyncio_current_task = asyncio.Task.current_task
+

 def random_port():
    """Get a single random port."""
@@ -79,8 +84,7 @@ def can_connect(ip, port):


 def make_ssl_context(keyfile, certfile, cafile=None, verify=True, check_hostname=True):
-    """Setup context for starting an https server or making requests over ssl.
-    """
+    """Setup context for starting an https server or making requests over ssl."""
    if not keyfile or not certfile:
        return None
    purpose = ssl.Purpose.SERVER_AUTH if verify else ssl.Purpose.CLIENT_AUTH
@@ -100,7 +104,7 @@ async def exponential_backoff(
    timeout=10,
    timeout_tolerance=0.1,
    *args,
-    **kwargs
+    **kwargs,
 ):
    """
    Exponentially backoff until `pass_func` is true.
@@ -175,7 +179,7 @@ async def exponential_backoff(
        dt = min(max_wait, remaining, random.uniform(0, start_wait * scale))
        if dt < max_wait:
            scale *= scale_factor
-        await gen.sleep(dt)
+        await asyncio.sleep(dt)
    raise TimeoutError(fail_message)


@@ -479,7 +483,7 @@ def print_stacks(file=sys.stderr):
    # also show asyncio tasks, if any
    # this will increase over time as we transition from tornado
    # coroutines to native `async def`
-    tasks = asyncio.Task.all_tasks()
+    tasks = asyncio_all_tasks()
    if tasks:
        print("AsyncIO tasks: %i" % len(tasks))
        for task in tasks:
@@ -507,28 +511,12 @@ def maybe_future(obj):
        return asyncio.wrap_future(obj)
    else:
        # could also check for tornado.concurrent.Future
-        # but with tornado >= 5 tornado.Future is asyncio.Future
+        # but with tornado >= 5.1 tornado.Future is asyncio.Future
        f = asyncio.Future()
        f.set_result(obj)
        return f


-@asynccontextmanager
-@async_generator
-async def not_aclosing(coro):
-    """An empty context manager for Python < 3.5.2
-    which lacks the `aclose` method on async iterators
-    """
-    await yield_(await coro)
-
-
-if sys.version_info < (3, 5, 2):
-    # Python 3.5.1 is missing the aclose method on async iterators,
-    # so we can't close them
-    aclosing = not_aclosing
-
-
-@async_generator
 async def iterate_until(deadline_future, generator):
    """An async generator that yields items from a generator
    until a deadline future resolves
@@ -553,7 +541,7 @@ async def iterate_until(deadline_future, generator):
            )
            if item_future.done():
                try:
-                    await yield_(item_future.result())
+                    yield item_future.result()
                except (StopAsyncIteration, asyncio.CancelledError):
                    break
            elif deadline_future.done():
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,2 +1,7 @@
 [tool.black]
 skip-string-normalization = true
+target_version = [
+    "py36",
+    "py37",
+    "py38",
+]
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,15 +1,15 @@
 alembic
-async_generator>=1.8
+async_generator>=1.9
 certipy>=0.1.2
 entrypoints
-jinja2
+jinja2>=2.11.0
 jupyter_telemetry>=0.1.0
 oauthlib>=3.0
-pamela
-prometheus_client>=0.0.21
+pamela; sys_platform != 'win32'
+prometheus_client>=0.4.0
 psutil>=5.6.5; sys_platform == 'win32'
 python-dateutil
 requests
 SQLAlchemy>=1.1
-tornado>=5.0
+tornado>=5.1
 traitlets>=4.3.2
--- a/setup.py
+++ b/setup.py
@@ -17,8 +17,8 @@ from setuptools.command.bdist_egg import bdist_egg


 v = sys.version_info
-if v[:2] < (3, 5):
-    error = "ERROR: JupyterHub requires Python version 3.5 or above."
+if v[:2] < (3, 6):
+    error = "ERROR: JupyterHub requires Python version 3.6 or above."
    print(error, file=sys.stderr)
    sys.exit(1)

@@ -94,7 +94,7 @@ setup_args = dict(
    license="BSD",
    platforms="Linux, Mac OS X",
    keywords=['Interactive', 'Interpreter', 'Shell', 'Web'],
-    python_requires=">=3.5",
+    python_requires=">=3.6",
    entry_points={
        'jupyterhub.authenticators': [
            'default = jupyterhub.auth:PAMAuthenticator',
--- a/share/jupyterhub/templates/login.html
+++ b/share/jupyterhub/templates/login.html
@@ -61,13 +61,25 @@
        id="login_submit"
        type="submit"
        class='btn btn-jupyter'
-        value='Sign In'
+        value='Sign in'
        tabindex="3"
        />
      <div class="feedback-widget hidden">
        <i class="fa fa-spinner"></i>
      </div>
    </div>
+
+    {% block login_terms %}
+    {% if login_term_url %}
+    <div id="login_terms" class="login_terms">
+    <input type="checkbox" id="login_terms_checkbox" name="login_terms_checkbox" required />
+    {% block login_terms_text %} {# allow overriding the text #}
+    By logging into the platform you accept the <a href="{{ login_term_url }}">terms and conditions</a>.
+    {% endblock login_terms_text %}
+    </div>
+    {% endif %}
+    {% endblock login_terms %}
+
  </div>
 </form>
 {% endif %}
--- a/tools/tasks.py
+++ b/tools/tasks.py
@@ -142,7 +142,7 @@ def untag(vs, push=False):

 def make_env(*packages):
    """Make a virtualenv
-    
+
    Assumes `which python` has the `virtualenv` package
    """
    if not os.path.exists(env_root):
@@ -167,7 +167,7 @@ def make_env(*packages):

 def build_sdist(py):
    """Build sdists
-    
+
    Returns the path to the tarball
    """
    with cd(repo_root):