consolidate trusted alt names

- trust subdomain_host by default
- JupyterHub.trusted_alt_names is inherited by Spawners by default. Do we need Spawner.ssl_alt_names to be separately configurable?

jupyterhub/app.py

@@ -1216,6 +1216,8 @@ class JupyterHub(Application):
                 self.internal_ssl_components_trust)
 
             default_alt_names = ["IP:127.0.0.1", "DNS:localhost"]
+            if self.subdomain_host:
+                default_alt_names.append("DNS:%s" % urlparse(self.subdomain_host).hostname)
             # The signed certs used by hub-internal components
             try:
                 internal_key_pair = certipy.store.get_record("hub-internal")

jupyterhub/spawner.py

@@ -28,7 +28,7 @@ from tornado.ioloop import PeriodicCallback
 from traitlets.config import LoggingConfigurable
 from traitlets import (
     Any, Bool, Dict, Instance, Integer, Float, List, Unicode, Union,
-    observe, validate,
+    default, observe, validate,
 )
 
 from .objects import Server
@@ -696,6 +696,8 @@ class Spawner(LoggingConfigurable):
         """
         return s.format(**self.template_namespace())
 
+    trusted_alt_names = List(Unicode())
+
     ssl_alt_names = List(
         Unicode(),
         config=True,
@@ -705,6 +707,13 @@ class Spawner(LoggingConfigurable):
         or set at runtime by Spawner that know their names.
         """
     )
+
+    @default('ssl_alt_names')
+    def _default_ssl_alt_names(self):
+        # by default, use trusted_alt_names
+        # inherited from global app
+        return list(self.trusted_alt_names)
+
     ssl_alt_names_include_local = Bool(
         True,
         config=True,

jupyterhub/utils.py

@@ -189,11 +189,9 @@ async def wait_for_http_server(url, timeout=10, ssl_context=None):
     """
     loop = ioloop.IOLoop.current()
     tic = loop.time()
-    settings = None
-    if ssl_context:
-        settings = {"ssl_options": ssl_context}
-    AsyncHTTPClient.configure(None, defaults=settings)
     client = AsyncHTTPClient()
+    if ssl_context:
+        client.ssl_options = ssl_context
     async def is_reachable():
         try:
             r = await client.fetch(url, follow_redirects=False)