login/logout of magpie as well (#17)

This unifies the login/logout capabilities of jupyterhub and magpie so
that when logging in to jupyterhub, the user is simultaneously logged in
to magpie. Similarly, when logging out of jupyterhub, the user is also
logged out of magpie.

This change requires that one additional parameter be set:
- `c.MagpieAuthenticator.public_fqdn` which is the publicly available
FQDN where magpie is running (this is required when setting the domain
on cookies)

Note:
- the `@gen.coroutine` decorator is replaced with the (now recommended)
`async` syntax

This change was first proposed here:
bird-house/birdhouse-deploy#358

jupyterhub_magpie_authenticator/jupyterhub_magpie_authenticator.py

@@ -1,33 +1,62 @@
 from traitlets import Unicode
 from jupyterhub.auth import Authenticator
-from tornado import gen
+from jupyterhub.handlers.login import LogoutHandler
 import requests
 
 
+class MagpieLogoutHandler(LogoutHandler):
+    """
+    Logout Handler that also logs the user out of magpie when logging out of jupyterhub.
+    """
+
+    async def handle_logout(self):
+        cookies = {key: morsel.coded_value for key, morsel in self.request.cookies.items()}
+        signout_url = self.authenticator.magpie_url.rstrip("/") + "/signout"
+        response = requests.get(signout_url, cookies=cookies, headers={"Host": self.authenticator.public_fqdn})
+        if response.ok and 'Set-Cookie' in response.headers:
+            self.set_header("Set-Cookie", response.headers["Set-Cookie"])
+
+
 class MagpieAuthenticator(Authenticator):
     """Authenticate to JupyterHub using Magpie.
 
     To use this authenticator, set the following parameters in the `jupyterhub_config.py` file:
      - c.JupyterHub.authenticator_class = 'jupyterhub_magpie_authenticator.MagpieAuthenticator'
-     - c.MagpieAuthenticator.magpie_url = "https://www.example.com/magpie"
+     - c.MagpieAuthenticator.magpie_url = "magpie:2000" # url where magpie is running (does not need to be public)
+     - c.MagpieAuthenticator.public_fqdn = "www.example.com"  # fqdn of server where magpie is running
     """
     default_provider = "ziggurat"
     magpie_url = Unicode(
         default_value="https://www.example.com/magpie",
         config=True,
         help="Magpie endpoint to signin to"
     )
+    public_fqdn = Unicode(
+        config=True,
+        help="Public fully qualified domain name. Used to set the magpie login cookie."
+    )
+
+    def get_handlers(self, app):
+        return [
+            ('/logout', MagpieLogoutHandler)
+        ]
 
-    @gen.coroutine
-    def authenticate(self, handler, data):
+    async def authenticate(self, handler, data):
         signin_url = self.magpie_url.rstrip('/') + '/signin'
-        
+
         post_data = {
             "user_name": data["username"],
             "password": data["password"],
             "provider_name": self.default_provider,
         }
         response = requests.post(signin_url, data=post_data)
-        
+
         if response.ok:
+            for cookie in response.cookies:
+                handler.set_cookie(name=cookie.name,
+                                   value=cookie.value,
+                                   domain=self.public_fqdn,
+                                   expires=cookie.expires,
+                                   path=cookie.path,
+                                   secure=cookie.secure)
             return data['username']