add options to require an access_token to GET /profile and /publicRooms on CS API (#5083)

This commit adds two config options:

* `restrict_public_rooms_to_local_users`

Requires auth to fetch the public rooms directory through the CS API and disables fetching it through the federation API.

* `require_auth_for_profile_requests`

When set to `true`, requires that requests to `/profile` over the CS API are authenticated, and only returns the user's profile if the requester shares a room with the profile's owner, as per MSC1301.

MSC1301 also specifies a behaviour for federation (only returning the profile if the server asking for it shares a room with the profile's owner), but that's currently really non-trivial to do in a not too expensive way. Next step is writing down a MSC that allows a HS to specify which user sent the profile query. In this implementation, Synapse won't send a profile query over federation if it doesn't believe it already shares a room with the profile's owner, though.

Groups have been intentionally omitted from this commit.

synapse/rest/client/v1/profile.py

@@ -31,11 +31,17 @@ class ProfileDisplaynameRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request, user_id):
+        requester_user = None
+
+        if self.hs.config.require_auth_for_profile_requests:
+            requester = yield self.auth.get_user_by_req(request)
+            requester_user = requester.user
+
         user = UserID.from_string(user_id)
 
-        displayname = yield self.profile_handler.get_displayname(
-            user,
-        )
+        yield self.profile_handler.check_profile_query_allowed(user, requester_user)
+
+        displayname = yield self.profile_handler.get_displayname(user)
 
         ret = {}
         if displayname is not None:
@@ -74,11 +80,17 @@ class ProfileAvatarURLRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request, user_id):
+        requester_user = None
+
+        if self.hs.config.require_auth_for_profile_requests:
+            requester = yield self.auth.get_user_by_req(request)
+            requester_user = requester.user
+
         user = UserID.from_string(user_id)
 
-        avatar_url = yield self.profile_handler.get_avatar_url(
-            user,
-        )
+        yield self.profile_handler.check_profile_query_allowed(user, requester_user)
+
+        avatar_url = yield self.profile_handler.get_avatar_url(user)
 
         ret = {}
         if avatar_url is not None:
@@ -116,14 +128,18 @@ class ProfileRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request, user_id):
+        requester_user = None
+
+        if self.hs.config.require_auth_for_profile_requests:
+            requester = yield self.auth.get_user_by_req(request)
+            requester_user = requester.user
+
         user = UserID.from_string(user_id)
 
-        displayname = yield self.profile_handler.get_displayname(
-            user,
-        )
-        avatar_url = yield self.profile_handler.get_avatar_url(
-            user,
-        )
+        yield self.profile_handler.check_profile_query_allowed(user, requester_user)
+
+        displayname = yield self.profile_handler.get_displayname(user)
+        avatar_url = yield self.profile_handler.get_avatar_url(user)
 
         ret = {}
         if displayname is not None:

synapse/rest/client/v1/room.py

@@ -301,6 +301,12 @@ class PublicRoomListRestServlet(ClientV1RestServlet):
         try:
             yield self.auth.get_user_by_req(request, allow_guest=True)
         except AuthError as e:
+            # Option to allow servers to require auth when accessing
+            # /publicRooms via CS API. This is especially helpful in private
+            # federations.
+            if self.hs.config.restrict_public_rooms_to_local_users:
+                raise
+
             # We allow people to not be authed if they're just looking at our
             # room list, but require auth when we proxy the request.
             # In both cases we call the auth function, as that has the side