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.

tests/rest/client/v1/test_rooms.py

@@ -904,3 +904,35 @@ class RoomSearchTestCase(unittest.HomeserverTestCase):
         self.assertEqual(
             context["profile_info"][self.other_user_id]["displayname"], "otheruser"
         )
+
+
+class PublicRoomsRestrictedTestCase(unittest.HomeserverTestCase):
+
+    servlets = [
+        admin.register_servlets,
+        room.register_servlets,
+        login.register_servlets,
+    ]
+
+    def make_homeserver(self, reactor, clock):
+
+        self.url = b"/_matrix/client/r0/publicRooms"
+
+        config = self.default_config()
+        config.restrict_public_rooms_to_local_users = True
+        self.hs = self.setup_test_homeserver(config=config)
+
+        return self.hs
+
+    def test_restricted_no_auth(self):
+        request, channel = self.make_request("GET", self.url)
+        self.render(request)
+        self.assertEqual(channel.code, 401, channel.result)
+
+    def test_restricted_auth(self):
+        self.register_user("user", "pass")
+        tok = self.login("user", "pass")
+
+        request, channel = self.make_request("GET", self.url, access_token=tok)
+        self.render(request)
+        self.assertEqual(channel.code, 200, channel.result)