Merge pull request #2342 from minrk/expire-auth

allow auth to expire

jupyterhub/auth.py

@@ -19,7 +19,7 @@ except Exception as e:
 from tornado.concurrent import run_on_executor
 
 from traitlets.config import LoggingConfigurable
-from traitlets import Bool, Set, Unicode, Dict, Any, default, observe
+from traitlets import Bool, Integer, Set, Unicode, Dict, Any, default, observe
 
 from .handlers.login import LoginHandler
 from .utils import maybe_future, url_path_join
@@ -50,6 +50,35 @@ class Authenticator(LoggingConfigurable):
         """,
     )
 
+    auth_refresh_age = Integer(
+        300,
+        config=True,
+        help="""The max age (in seconds) of authentication info
+        before forcing a refresh of user auth info.
+
+        Refreshing auth info allows, e.g. requesting/re-validating auth tokens.
+
+        See :meth:`.refresh_user` for what happens when user auth info is refreshed
+        (nothing by default).
+        """
+    )
+
+    refresh_pre_spawn = Bool(
+        False,
+        config=True,
+        help="""Force refresh of auth prior to spawn.
+
+        This forces :meth:`.refresh_user` to be called prior to launching
+        a server, to ensure that auth state is up-to-date.
+
+        This can be important when e.g. auth tokens that may have expired
+        are passed to the spawner via environment variables from auth_state.
+
+        If refresh_user cannot refresh the user auth data,
+        launch will fail until the user logs in again.
+        """
+    )
+
     admin_users = Set(
         help="""
         Set of users that will have admin rights on this JupyterHub.

jupyterhub/handlers/base.py

@@ -28,6 +28,7 @@ from .. import __version__
 from .. import orm
 from ..objects import Server
 from ..spawner import LocalProcessSpawner
+from ..user import User
 from ..utils import maybe_future, url_path_join
 from ..metrics import (
     SERVER_SPAWN_DURATION_SECONDS, ServerSpawnStatus,
@@ -240,7 +241,7 @@ class BaseHandler(RequestHandler):
         self.db.commit()
         return self._user_from_orm(orm_token.user)
 
-    async def refresh_user_auth(self, user, force=False):
+    async def refresh_auth(self, user, force=False):
         """Refresh user authentication info
 
         Calls `authenticator.refresh_user(user)`
@@ -254,7 +255,12 @@ class BaseHandler(RequestHandler):
             user (User): the user having been refreshed,
                 or None if the user must login again to refresh auth info.
         """
-        if not force: # TODO: and it's sufficiently recent
+        refresh_age = self.authenticator.auth_refresh_age
+        if not refresh_age:
+            return user
+        now = time.monotonic()
+        if not force and user._auth_refreshed and (now - user._auth_refreshed < refresh_age):
+            # auth up-to-date
             return user
 
         # refresh a user at most once per request
@@ -275,6 +281,8 @@ class BaseHandler(RequestHandler):
             )
             return
 
+        user._auth_refreshed = now
+
         if auth_info == True:
             # refresh_user confirmed that it's up-to-date,
             # nothing to refresh
@@ -355,8 +363,8 @@ class BaseHandler(RequestHandler):
                 user = self.get_current_user_token()
                 if user is None:
                     user = self.get_current_user_cookie()
-                if user:
-                    user = await self.refresh_user_auth(user)
+                if user and isinstance(user, User):
+                    user = await self.refresh_auth(user)
                 self._jupyterhub_user = user
             except Exception:
                 # don't let errors here raise more than once
@@ -610,6 +618,7 @@ class BaseHandler(RequestHandler):
             self.statsd.incr('login.success')
             self.statsd.timing('login.authenticate.success', auth_timer.ms)
             self.log.info("User logged in: %s", user.name)
+            user._auth_refreshed = time.monotonic()
             return user
         else:
             self.statsd.incr('login.failure')
@@ -643,6 +652,11 @@ class BaseHandler(RequestHandler):
 
     async def spawn_single_user(self, user, server_name='', options=None):
         # in case of error, include 'try again from /hub/home' message
+        if self.authenticator.refresh_pre_spawn:
+            auth_user = await self.refresh_auth(user, force=True)
+            if auth_user is None:
+                raise web.HTTPError(403, "auth has expired for %s, login again", user.name)
+
         spawn_start_time = time.perf_counter()
         self.extra_error_html = self.spawn_home_error
 

jupyterhub/services/service.py

@@ -258,7 +258,6 @@ class Service(LoggingConfigurable):
     def _default_redirect_uri(self):
         if self.server is None:
             return ''
-        print(self.domain, self.host, self.server)
         return self.host + url_path_join(self.prefix, 'oauth_callback')
 
     @property

jupyterhub/tests/conftest.py

@@ -47,7 +47,7 @@ from ..utils import random_port
 
 from . import mocking
 from .mocking import MockHub
-from .utils import ssl_setup
+from .utils import ssl_setup, add_user
 from .test_services import mockservice_cmd
 
 import jupyterhub.services.service
@@ -185,6 +185,43 @@ def cleanup_after(request, io_loop):
         app.db.commit()
 
 
+_username_counter = 0
+
+
+def new_username(prefix='testuser'):
+    """Return a new unique username"""
+    global _username_counter
+    _username_counter += 1
+    return '{}-{}'.format(prefix, _username_counter)
+
+
+@fixture
+def username():
+    """allocate a temporary username
+
+    unique each time the fixture is used
+    """
+    yield new_username()
+
+
+@fixture
+def user(app):
+    """Fixture for creating a temporary user
+
+    Each time the fixture is used, a new user is created
+    """
+    user = add_user(app.db, app, name=new_username())
+    yield user
+
+
+@fixture
+def admin_user(app, username):
+    """Fixture for creating a temporary admin user"""
+    user = add_user(app.db, app, name=new_username('testadmin'), admin=True)
+    yield user
+
+
+
 class MockServiceSpawner(jupyterhub.services.service._ServiceSpawner):
     """mock services for testing.
 

jupyterhub/tests/mocking.py

@@ -49,7 +49,7 @@ from ..objects import Server
 from ..spawner import LocalProcessSpawner, SimpleLocalProcessSpawner
 from ..singleuser import SingleUserNotebookApp
 from ..utils import random_port, url_path_join
-from .utils import async_requests, ssl_setup
+from .utils import async_requests, ssl_setup, public_host, public_url
 
 from pamela import PAMError
 
@@ -223,7 +223,10 @@ class MockHub(JupyterHub):
     last_activity_interval = 2
     log_datefmt = '%M:%S'
     external_certs = None
-    log_level = 10
+
+    @default('log_level')
+    def _default_log_level(self):
+        return 10
 
     def __init__(self, *args, **kwargs):
         if 'internal_certs_location' in kwargs:
@@ -351,31 +354,6 @@ class MockHub(JupyterHub):
         return r.cookies
 
 
-def public_host(app):
-    """Return the public *host* (no URL prefix) of the given JupyterHub instance."""
-    if app.subdomain_host:
-        return app.subdomain_host
-    else:
-        return Server.from_url(app.proxy.public_url).host
-
-
-def public_url(app, user_or_service=None, path=''):
-    """Return the full, public base URL (including prefix) of the given JupyterHub instance."""
-    if user_or_service:
-        if app.subdomain_host:
-            host = user_or_service.host
-        else:
-            host = public_host(app)
-        prefix = user_or_service.prefix
-    else:
-        host = public_host(app)
-        prefix = Server.from_url(app.proxy.public_url).base_url
-    if path:
-        return host + url_path_join(prefix, path)
-    else:
-        return host + prefix
-
-
 # single-user-server mocking:
 
 class MockSingleUserServer(SingleUserNotebookApp):

jupyterhub/tests/test_api.py

@@ -18,97 +18,13 @@ import jupyterhub
 from .. import orm
 from ..utils import url_path_join as ujoin
 from .mocking import public_host, public_url
-from .utils import async_requests
-
-
-def check_db_locks(func):
-    """Decorator that verifies no locks are held on database upon exit.
-
-    This decorator for test functions verifies no locks are held on the
-    application's database upon exit by creating and dropping a dummy table.
-
-    The decorator relies on an instance of JupyterHubApp being the first
-    argument to the decorated function.
-
-    Example
-    -------
-
-        @check_db_locks
-        def api_request(app, *api_path, **kwargs):
-
-    """
-    def new_func(app, *args, **kwargs):
-        retval = func(app, *args, **kwargs)
-
-        temp_session = app.session_factory()
-        temp_session.execute('CREATE TABLE dummy (foo INT)')
-        temp_session.execute('DROP TABLE dummy')
-        temp_session.close()
-
-        return retval
-
-    return new_func
-
-
-def find_user(db, name, app=None):
-    """Find user in database."""
-    orm_user = db.query(orm.User).filter(orm.User.name == name).first()
-    if app is None:
-        return orm_user
-    else:
-        return app.users[orm_user.id]
-
-
-def add_user(db, app=None, **kwargs):
-    """Add a user to the database."""
-    orm_user = find_user(db, name=kwargs.get('name'))
-    if orm_user is None:
-        orm_user = orm.User(**kwargs)
-        db.add(orm_user)
-    else:
-        for attr, value in kwargs.items():
-            setattr(orm_user, attr, value)
-    db.commit()
-    if app:
-        return app.users[orm_user.id]
-    else:
-        return orm_user
-
-
-def auth_header(db, name):
-    """Return header with user's API authorization token."""
-    user = find_user(db, name)
-    if user is None:
-        user = add_user(db, name=name)
-    token = user.new_api_token()
-    return {'Authorization': 'token %s' % token}
-
-
-@check_db_locks
-async def api_request(app, *api_path, **kwargs):
-    """Make an API request"""
-    base_url = app.hub.url
-    headers = kwargs.setdefault('headers', {})
-
-    if 'Authorization' not in headers and not kwargs.pop('noauth', False):
-        # make a copy to avoid modifying arg in-place
-        kwargs['headers'] = h = {}
-        h.update(headers)
-        h.update(auth_header(app.db, 'admin'))
-
-    url = ujoin(base_url, 'api', *api_path)
-    method = kwargs.pop('method', 'get')
-    f = getattr(async_requests, method)
-    if app.internal_ssl:
-        kwargs['cert'] = (app.internal_ssl_cert, app.internal_ssl_key)
-        kwargs["verify"] = app.internal_ssl_ca
-    resp = await f(url, **kwargs)
-    assert "frame-ancestors 'self'" in resp.headers['Content-Security-Policy']
-    assert ujoin(app.hub.base_url, "security/csp-report") in resp.headers['Content-Security-Policy']
-    assert 'http' not in resp.headers['Content-Security-Policy']
-    if not kwargs.get('stream', False) and resp.content:
-        assert resp.headers.get('content-type') == 'application/json'
-    return resp
+from .utils import (
+    add_user,
+    api_request,
+    async_requests,
+    auth_header,
+    find_user,
+)
 
 
 # --------------------
@@ -197,7 +113,7 @@ def normalize_timestamp(ts):
     """
     if ts is None:
         return
-    return re.sub('\d(\.\d+)?', '0', ts)
+    return re.sub(r'\d(\.\d+)?', '0', ts)
 
 
 def normalize_user(user):

jupyterhub/tests/test_auth.py

@@ -12,7 +12,8 @@ from requests import HTTPError
 from jupyterhub import auth, crypto, orm
 
 from .mocking import MockPAMAuthenticator, MockStructGroup, MockStructPasswd
-from .test_api import add_user
+from .utils import add_user
+
 
 async def test_pam_auth():
     authenticator = MockPAMAuthenticator()

jupyterhub/tests/test_auth_expiry.py

@@ -0,0 +1,179 @@
+"""
+test authentication expiry
+
+authentication can expire in a number of ways:
+
+- needs refresh and can be refreshed
+- doesn't need refresh
+- needs refresh and cannot be refreshed without new login
+"""
+
+import asyncio
+from contextlib import contextmanager
+from unittest import mock
+from urllib.parse import parse_qs, urlparse
+
+import pytest
+
+from .utils import api_request, get_page
+
+
+async def refresh_expired(authenticator, user):
+    return None
+
+
+@pytest.fixture
+def disable_refresh(app):
+    """Fixture disabling auth refresh"""
+    with mock.patch.object(app.authenticator, 'refresh_user', refresh_expired):
+        yield
+
+
+@pytest.fixture
+def refresh_pre_spawn(app):
+    """Fixture enabling auth refresh pre spawn"""
+    app.authenticator.refresh_pre_spawn = True
+    try:
+        yield
+    finally:
+        app.authenticator.refresh_pre_spawn = False
+
+
+async def test_auth_refresh_at_login(app, user):
+    # auth_refreshed starts unset:
+    assert not user._auth_refreshed
+    # login sets auth_refreshed timestamp
+    await app.login_user(user.name)
+    assert user._auth_refreshed
+    user._auth_refreshed -= 10
+    before = user._auth_refreshed
+    # login again updates auth_refreshed timestamp
+    # even when auth is fresh
+    await app.login_user(user.name)
+    assert user._auth_refreshed > before
+
+
+async def test_auth_refresh_page(app, user):
+    cookies = await app.login_user(user.name)
+    assert user._auth_refreshed
+    user._auth_refreshed -= 10
+    before = user._auth_refreshed
+
+    # get a page with auth not expired
+    # doesn't trigger refresh
+    r = await get_page('home', app, cookies=cookies)
+    assert r.status_code == 200
+    assert user._auth_refreshed == before
+
+    # get a page with stale auth, refreshes auth
+    user._auth_refreshed -= app.authenticator.auth_refresh_age
+    r = await get_page('home', app, cookies=cookies)
+    assert r.status_code == 200
+    assert user._auth_refreshed > before
+
+
+async def test_auth_expired_page(app, user, disable_refresh):
+    cookies = await app.login_user(user.name)
+    assert user._auth_refreshed
+    user._auth_refreshed -= 10
+    before = user._auth_refreshed
+
+    # auth is fresh, doesn't trigger expiry
+    r = await get_page('home', app, cookies=cookies)
+    assert user._auth_refreshed == before
+    assert r.status_code == 200
+
+    # get a page with stale auth, triggers expiry
+    user._auth_refreshed -= app.authenticator.auth_refresh_age
+    before = user._auth_refreshed
+    r = await get_page('home', app, cookies=cookies, allow_redirects=False)
+
+    # verify that we redirect to login with ?next=requested page
+    assert r.status_code == 302
+    redirect_url = urlparse(r.headers['Location'])
+    assert redirect_url.path.endswith('/login')
+    query = parse_qs(redirect_url.query)
+    assert query['next']
+    next_url = urlparse(query['next'][0])
+    assert next_url.path == urlparse(r.url).path
+
+    # make sure refresh didn't get updated
+    assert user._auth_refreshed == before
+
+
+async def test_auth_expired_api(app, user, disable_refresh):
+    cookies = await app.login_user(user.name)
+    assert user._auth_refreshed
+    user._auth_refreshed -= 10
+    before = user._auth_refreshed
+
+    # auth is fresh, doesn't trigger expiry
+    r = await api_request(app, 'users/' + user.name, name=user.name)
+    assert user._auth_refreshed == before
+    assert r.status_code == 200
+
+    # get a page with stale auth, triggers expiry
+    user._auth_refreshed -= app.authenticator.auth_refresh_age
+    r = await api_request(app, 'users/' + user.name, name=user.name)
+    # api requests can't do login redirects
+    assert r.status_code == 403
+
+
+async def test_refresh_pre_spawn(app, user, refresh_pre_spawn):
+    cookies = await app.login_user(user.name)
+    assert user._auth_refreshed
+    user._auth_refreshed -= 10
+    before = user._auth_refreshed
+
+    # auth is fresh, but should be forced to refresh by spawn
+    r = await api_request(
+        app, 'users/{}/server'.format(user.name), method='post', name=user.name
+    )
+    assert 200 <= r.status_code < 300
+    assert user._auth_refreshed > before
+
+
+async def test_refresh_pre_spawn_expired(app, user, refresh_pre_spawn, disable_refresh):
+    cookies = await app.login_user(user.name)
+    assert user._auth_refreshed
+    user._auth_refreshed -= 10
+    before = user._auth_refreshed
+
+    # auth is fresh, doesn't trigger expiry
+    r = await api_request(
+        app, 'users/{}/server'.format(user.name), method='post', name=user.name
+    )
+    assert r.status_code == 403
+    assert user._auth_refreshed == before
+
+
+async def test_refresh_pre_spawn_admin_request(
+    app, user, admin_user, refresh_pre_spawn
+):
+    await app.login_user(user.name)
+    await app.login_user(admin_user.name)
+    user._auth_refreshed -= 10
+    before = user._auth_refreshed
+
+    # admin request, auth is fresh. Should still refresh user auth.
+    r = await api_request(
+        app, 'users', user.name, 'server', method='post', name=admin_user.name
+    )
+    assert 200 <= r.status_code < 300
+    assert user._auth_refreshed > before
+
+
+async def test_refresh_pre_spawn_expired_admin_request(
+    app, user, admin_user, refresh_pre_spawn, disable_refresh
+):
+    await app.login_user(user.name)
+    await app.login_user(admin_user.name)
+    user._auth_refreshed -= 10
+
+    # auth needs refresh but can't without a new login; spawn should fail
+    user._auth_refreshed -= app.authenticator.auth_refresh_age
+    r = await api_request(
+        app, 'users', user.name, 'server', method='post', name=admin_user.name
+    )
+    # api requests can't do login redirects
+    assert r.status_code == 403

jupyterhub/tests/test_pages.py

@@ -2,6 +2,7 @@
 
 import asyncio
 import sys
+from unittest import mock
 from urllib.parse import urlencode, urlparse
 
 from bs4 import BeautifulSoup
@@ -13,21 +14,17 @@ from ..utils import url_path_join as ujoin
 from .. import orm
 from ..auth import Authenticator
 
-import mock
 import pytest
 
-from .mocking import FormSpawner, public_url, public_host
-from .test_api import api_request, add_user
-from .utils import async_requests
-
-
-def get_page(path, app, hub=True, **kw):
-    if hub:
-        prefix = app.hub.base_url
-    else:
-        prefix = app.base_url
-    base_url = ujoin(public_host(app), prefix)
-    return async_requests.get(ujoin(base_url, path), **kw)
+from .mocking import FormSpawner
+from .utils import (
+    async_requests,
+    api_request,
+    add_user,
+    get_page,
+    public_url,
+    public_host,
+)
 
 
 async def test_root_no_auth(app):

jupyterhub/tests/test_proxy.py

@@ -84,7 +84,8 @@ async def test_external_proxy(request):
     # add user to the db and start a single user server
     name = 'river'
     add_user(app.db, app, name=name)
-    r = await api_request(app, 'users', name, 'server', method='post')
+    r = await api_request(app, 'users', name, 'server', method='post',
+                          bypass_proxy=True)
     r.raise_for_status()
 
     routes = await app.proxy.get_all_routes()
@@ -108,7 +109,7 @@ async def test_external_proxy(request):
     assert list(routes.keys()) == []
 
     # poke the server to update the proxy
-    r = await api_request(app, 'proxy', method='post')
+    r = await api_request(app, 'proxy', method='post', bypass_proxy=True)
     r.raise_for_status()
 
     # check that the routes are correct
@@ -135,10 +136,16 @@ async def test_external_proxy(request):
 
     # tell the hub where the new proxy is
     new_api_url = 'http://{}:{}'.format(proxy_ip, proxy_port)
-    r = await api_request(app, 'proxy', method='patch', data=json.dumps({
-        'api_url': new_api_url,
-        'auth_token': new_auth_token,
-    }))
+    r = await api_request(
+        app,
+        'proxy',
+        method='patch',
+        data=json.dumps({
+            'api_url': new_api_url,
+            'auth_token': new_auth_token,
+        }),
+        bypass_proxy=True,
+    )
     r.raise_for_status()
     assert app.proxy.api_url == new_api_url
 

jupyterhub/tests/utils.py

@@ -4,6 +4,10 @@ from concurrent.futures import ThreadPoolExecutor
 from certipy import Certipy
 import requests
 
+from jupyterhub import orm
+from jupyterhub.objects import Server
+from jupyterhub.utils import url_path_join as ujoin
+
 
 class _AsyncRequests:
     """Wrapper around requests to return a Future from request methods
@@ -46,3 +50,144 @@ def ssl_setup(cert_dir, authority_name):
         "external", authority_name, overwrite=True, alt_names=alt_names
     )
     return external_certs
+
+
+def check_db_locks(func):
+    """Decorator that verifies no locks are held on database upon exit.
+
+    This decorator for test functions verifies no locks are held on the
+    application's database upon exit by creating and dropping a dummy table.
+
+    The decorator relies on an instance of JupyterHubApp being the first
+    argument to the decorated function.
+
+    Example
+    -------
+
+        @check_db_locks
+        def api_request(app, *api_path, **kwargs):
+
+    """
+    def new_func(app, *args, **kwargs):
+        retval = func(app, *args, **kwargs)
+
+        temp_session = app.session_factory()
+        temp_session.execute('CREATE TABLE dummy (foo INT)')
+        temp_session.execute('DROP TABLE dummy')
+        temp_session.close()
+
+        return retval
+
+    return new_func
+
+
+def find_user(db, name, app=None):
+    """Find user in database."""
+    orm_user = db.query(orm.User).filter(orm.User.name == name).first()
+    if app is None:
+        return orm_user
+    else:
+        return app.users[orm_user.id]
+
+
+def add_user(db, app=None, **kwargs):
+    """Add a user to the database."""
+    orm_user = find_user(db, name=kwargs.get('name'))
+    if orm_user is None:
+        orm_user = orm.User(**kwargs)
+        db.add(orm_user)
+    else:
+        for attr, value in kwargs.items():
+            setattr(orm_user, attr, value)
+    db.commit()
+    if app:
+        return app.users[orm_user.id]
+    else:
+        return orm_user
+
+
+def auth_header(db, name):
+    """Return header with user's API authorization token."""
+    user = find_user(db, name)
+    if user is None:
+        user = add_user(db, name=name)
+    token = user.new_api_token()
+    return {'Authorization': 'token %s' % token}
+
+
+@check_db_locks
+async def api_request(app, *api_path, method='get',
+                      noauth=False, bypass_proxy=False,
+                      **kwargs):
+    """Make an API request"""
+    if bypass_proxy:
+        # make a direct request to the hub,
+        # skipping the proxy
+        base_url = app.hub.url
+    else:
+        base_url = public_url(app, path='hub')
+    headers = kwargs.setdefault('headers', {})
+
+    if (
+        'Authorization' not in headers
+        and not noauth
+        and 'cookies' not in kwargs
+    ):
+        # make a copy to avoid modifying arg in-place
+        kwargs['headers'] = h = {}
+        h.update(headers)
+        h.update(auth_header(app.db, kwargs.pop('name', 'admin')))
+
+    if 'cookies' in kwargs:
+        # for cookie-authenticated requests,
+        # set Referer so it looks like the request originated
+        # from a Hub-served page
+        headers.setdefault('Referer', ujoin(base_url, 'test'))
+
+    url = ujoin(base_url, 'api', *api_path)
+    f = getattr(async_requests, method)
+    if app.internal_ssl:
+        kwargs['cert'] = (app.internal_ssl_cert, app.internal_ssl_key)
+        kwargs["verify"] = app.internal_ssl_ca
+    resp = await f(url, **kwargs)
+    assert "frame-ancestors 'self'" in resp.headers['Content-Security-Policy']
+    assert ujoin(app.hub.base_url, "security/csp-report") in resp.headers['Content-Security-Policy']
+    assert 'http' not in resp.headers['Content-Security-Policy']
+    if not kwargs.get('stream', False) and resp.content:
+        assert resp.headers.get('content-type') == 'application/json'
+    return resp
+
+
+def get_page(path, app, hub=True, **kw):
+    if hub:
+        prefix = app.hub.base_url
+    else:
+        prefix = app.base_url
+    base_url = ujoin(public_host(app), prefix)
+    return async_requests.get(ujoin(base_url, path), **kw)
+
+
+def public_host(app):
+    """Return the public *host* (no URL prefix) of the given JupyterHub instance."""
+    if app.subdomain_host:
+        return app.subdomain_host
+    else:
+        return Server.from_url(app.proxy.public_url).host
+
+
+def public_url(app, user_or_service=None, path=''):
+    """Return the full, public base URL (including prefix) of the given JupyterHub instance."""
+    if user_or_service:
+        if app.subdomain_host:
+            host = user_or_service.host
+        else:
+            host = public_host(app)
+        prefix = user_or_service.prefix
+    else:
+        host = public_host(app)
+        prefix = Server.from_url(app.proxy.public_url).base_url
+    if path:
+        return host + ujoin(prefix, path)
+    else:
+        return host + prefix
+

jupyterhub/user.py

@@ -8,7 +8,9 @@ import warnings
 
 from sqlalchemy import inspect
 from tornado import gen
+from tornado.httputil import urlencode
 from tornado.log import app_log
+from tornado import web
 
 from .utils import maybe_future, url_path_join, make_ssl_context
 
@@ -136,6 +138,7 @@ class User:
     orm_user = None
     log = app_log
     settings = None
+    _auth_refreshed = None
 
     def __init__(self, orm_user, settings=None, db=None):
         self.db = db or inspect(orm_user).session
@@ -380,6 +383,59 @@ class User:
             url_parts.extend(['server/progress'])
         return url_path_join(*url_parts)
 
+    async def refresh_auth(self, handler):
+        """Refresh authentication if needed
+
+        Checks authentication expiry and refresh it if needed.
+        See Spawner.
+
+        If the auth is expired and cannot be refreshed
+        without forcing a new login, a few things can happen:
+
+        1. if this is a normal user spawn,
+           the user should be redirected to login
+           and back to spawn after login.
+        2. if this is a spawn via API or other user,
+           spawn will fail until the user logs in again.
+
+        Args:
+            handler (RequestHandler):
+                The handler for the request triggering the spawn.
+                May be None
+        """
+        authenticator = self.authenticator
+        if authenticator is None or not authenticator.refresh_pre_spawn:
+            # nothing to do
+            return
+
+        # refresh auth
+        auth_user = await handler.refresh_auth(self, force=True)
+
+        if auth_user:
+            # auth refreshed, all done
+            return
+
+        # if we got to here, auth is expired and couldn't be refreshed
+        self.log.error(
+            "Auth expired for %s; cannot spawn until they login again",
+            self.name,
+        )
+        # auth expired, cannot spawn without a fresh login
+        # it's the current user *and* spawn via GET, trigger login redirect
+        if handler.request.method == 'GET' and handler.current_user is self:
+            self.log.info("Redirecting %s to login to refresh auth", self.name)
+            url = self.get_login_url()
+            next_url = self.request.uri
+            sep = '&' if '?' in url else '?'
+            url += sep + urlencode(dict(next=next_url))
+            self.redirect(url)
+            raise web.Finish()
+        else:
+            # spawn via POST or on behalf of another user.
+            # nothing we can do here but fail
+            raise web.HTTPError(400, "{}'s authentication has expired".format(self.name))
+
+
     async def spawn(self, server_name='', options=None, handler=None):
         """Start the user's spawner
 
@@ -395,6 +451,9 @@ class User:
         """
         db = self.db
 
+        if handler:
+            await self.refresh_auth(handler)
+
         base_url = url_path_join(self.base_url, server_name) + '/'
 
         orm_server = orm.Server(
@@ -436,7 +495,7 @@ class User:
 
         # trigger pre-spawn hook on authenticator
         authenticator = self.authenticator
-        if (authenticator):
+        if authenticator:
             await maybe_future(authenticator.pre_spawn_start(self, spawner))
 
         spawner._start_pending = True