Exchange 3pid invites for m.room.member invites

synapse/api/auth.py

@@ -24,7 +24,6 @@ from synapse.api.constants import EventTypes, Membership, JoinRules
 from synapse.api.errors import AuthError, Codes, SynapseError, EventSizeError
 from synapse.types import RoomID, UserID, EventID
 from synapse.util.logutils import log_function
-from synapse.util import third_party_invites
 from unpaddedbase64 import decode_base64
 
 import logging
@@ -318,6 +317,11 @@ class Auth(object):
             }
         )
 
+        if Membership.INVITE == membership and "third_party_invite" in event.content:
+            if not self._verify_third_party_invite(event, auth_events):
+                raise AuthError(403, "You are not invited to this room.")
+            return True
+
         if Membership.JOIN != membership:
             if (caller_invited
                     and Membership.LEAVE == membership
@@ -361,7 +365,6 @@ class Auth(object):
                 pass
             elif join_rule == JoinRules.INVITE:
                 if not caller_in_room and not caller_invited:
-                    if not self._verify_third_party_invite(event, auth_events):
                     raise AuthError(403, "You are not invited to this room.")
             else:
                 # TODO (erikj): may_join list
@@ -390,10 +393,10 @@ class Auth(object):
 
     def _verify_third_party_invite(self, event, auth_events):
         """
-        Validates that the join event is authorized by a previous third-party invite.
+        Validates that the invite event is authorized by a previous third-party invite.
 
-        Checks that the public key, and keyserver, match those in the invite,
+        Checks that the public key, and keyserver, match those in the third party invite,
-        and that the join event has a signature issued using that public key.
+        and that the invite event has a signature issued using that public key.
 
         Args:
             event: The m.room.member join event being validated.
@@ -404,35 +407,28 @@ class Auth(object):
             True if the event fulfills the expectations of a previous third party
             invite event.
         """
-        if not third_party_invites.join_has_third_party_invite(event.content):
+        if "third_party_invite" not in event.content:
             return False
-        join_third_party_invite = event.content["third_party_invite"]
+        if "signed" not in event.content["third_party_invite"]:
-        token = join_third_party_invite["token"]
+            return False
+        signed = event.content["third_party_invite"]["signed"]
+        for key in {"mxid", "token"}:
+            if key not in signed:
+                return False
+
+        token = signed["token"]
+
         invite_event = auth_events.get(
             (EventTypes.ThirdPartyInvite, token,)
         )
         if not invite_event:
-            logger.info("Failing 3pid invite because no invite found for token %s", token)
+            return False
+
+        if event.user_id != invite_event.user_id:
             return False
         try:
-            public_key = join_third_party_invite["public_key"]
+            public_key = invite_event.content["public_key"]
-            key_validity_url = join_third_party_invite["key_validity_url"]
+            if signed["mxid"] != event.state_key:
-            if invite_event.content["public_key"] != public_key:
-                logger.info(
-                    "Failing 3pid invite because public key invite: %s != join: %s",
-                    invite_event.content["public_key"],
-                    public_key
-                )
-                return False
-            if invite_event.content["key_validity_url"] != key_validity_url:
-                logger.info(
-                    "Failing 3pid invite because key_validity_url invite: %s != join: %s",
-                    invite_event.content["key_validity_url"],
-                    key_validity_url
-                )
-                return False
-            signed = join_third_party_invite["signed"]
-            if signed["mxid"] != event.user_id:
                 return False
             if signed["token"] != token:
                 return False
@@ -445,6 +441,11 @@ class Auth(object):
                         decode_base64(public_key)
                     )
                     verify_signed_json(signed, server, verify_key)
+
+                    # We got the public key from the invite, so we know that the
+                    # correct server signed the signed bundle.
+                    # The caller is responsible for checking that the signing
+                    # server has not revoked that public key.
                     return True
             return False
         except (KeyError, SignatureVerifyException,):
@@ -751,17 +752,19 @@ class Auth(object):
             if e_type == Membership.JOIN:
                 if member_event and not is_public:
                     auth_ids.append(member_event.event_id)
-                if third_party_invites.join_has_third_party_invite(event.content):
+            else:
+                if member_event:
+                    auth_ids.append(member_event.event_id)
+
+            if e_type == Membership.INVITE:
+                if "third_party_invite" in event.content:
                     key = (
                         EventTypes.ThirdPartyInvite,
                         event.content["third_party_invite"]["token"]
                     )
-                    invite = current_state.get(key)
+                    third_party_invite = current_state.get(key)
-                    if invite:
+                    if third_party_invite:
-                        auth_ids.append(invite.event_id)
+                        auth_ids.append(third_party_invite.event_id)
-            else:
-                if member_event:
-                    auth_ids.append(member_event.event_id)
         elif member_event:
             if member_event.content["membership"] == Membership.JOIN:
                 auth_ids.append(member_event.event_id)

synapse/federation/federation_client.py

@@ -26,7 +26,6 @@ from synapse.api.errors import (
 from synapse.util import unwrapFirstError
 from synapse.util.caches.expiringcache import ExpiringCache
 from synapse.util.logutils import log_function
-from synapse.util import third_party_invites
 from synapse.events import FrozenEvent
 import synapse.metrics
 
@@ -358,7 +357,7 @@ class FederationClient(FederationBase):
         defer.returnValue(signed_auth)
 
     @defer.inlineCallbacks
-    def make_membership_event(self, destinations, room_id, user_id, membership, content):
+    def make_membership_event(self, destinations, room_id, user_id, membership):
         """
         Creates an m.room.member event, with context, without participating in the room.
 
@@ -390,14 +389,9 @@ class FederationClient(FederationBase):
             if destination == self.server_name:
                 continue
 
-            args = {}
-            if third_party_invites.join_has_third_party_invite(content):
-                args = third_party_invites.extract_join_keys(
-                    content["third_party_invite"]
-                )
             try:
                 ret = yield self.transport_layer.make_membership_event(
-                    destination, room_id, user_id, membership, args
+                    destination, room_id, user_id, membership
                 )
 
                 pdu_dict = ret["event"]
@@ -704,3 +698,26 @@ class FederationClient(FederationBase):
         event.internal_metadata.outlier = outlier
 
         return event
+
+    @defer.inlineCallbacks
+    def forward_third_party_invite(self, destinations, room_id, event_dict):
+        for destination in destinations:
+            if destination == self.server_name:
+                continue
+
+            try:
+                yield self.transport_layer.exchange_third_party_invite(
+                    destination=destination,
+                    room_id=room_id,
+                    event_dict=event_dict,
+                )
+                defer.returnValue(None)
+            except CodeMessageException:
+                raise
+            except Exception as e:
+                logger.exception(
+                    "Failed to send_third_party_invite via %s: %s",
+                    destination, e.message
+                )
+
+        raise RuntimeError("Failed to send to any server.")

synapse/federation/federation_server.py

@@ -23,12 +23,10 @@ from synapse.util.logutils import log_function
 from synapse.events import FrozenEvent
 import synapse.metrics
 
-from synapse.api.errors import FederationError, SynapseError, Codes
+from synapse.api.errors import FederationError, SynapseError
 
 from synapse.crypto.event_signing import compute_event_signature
 
-from synapse.util import third_party_invites
-
 import simplejson as json
 import logging
 
@@ -230,19 +228,8 @@ class FederationServer(FederationBase):
             )
 
     @defer.inlineCallbacks
-    def on_make_join_request(self, room_id, user_id, query):
+    def on_make_join_request(self, room_id, user_id):
-        threepid_details = {}
+        pdu = yield self.handler.on_make_join_request(room_id, user_id)
-        if third_party_invites.has_join_keys(query):
-            for k in third_party_invites.JOIN_KEYS:
-                if not isinstance(query[k], list) or len(query[k]) != 1:
-                    raise FederationError(
-                        "FATAL",
-                        Codes.MISSING_PARAM,
-                        "key %s value %s" % (k, query[k],),
-                        None
-                    )
-                threepid_details[k] = query[k][0]
-        pdu = yield self.handler.on_make_join_request(room_id, user_id, threepid_details)
         time_now = self._clock.time_msec()
         defer.returnValue({"event": pdu.get_pdu_json(time_now)})
 
@@ -556,3 +543,15 @@ class FederationServer(FederationBase):
         event.internal_metadata.outlier = outlier
 
         return event
+
+    @defer.inlineCallbacks
+    def exchange_third_party_invite(self, invite):
+        ret = yield self.handler.exchange_third_party_invite(invite)
+        defer.returnValue(ret)
+
+    @defer.inlineCallbacks
+    def on_exchange_third_party_invite_request(self, origin, room_id, event_dict):
+        ret = yield self.handler.on_exchange_third_party_invite_request(
+            origin, room_id, event_dict
+        )
+        defer.returnValue(ret)

synapse/federation/transport/client.py

@@ -161,7 +161,7 @@ class TransportLayerClient(object):
 
     @defer.inlineCallbacks
     @log_function
-    def make_membership_event(self, destination, room_id, user_id, membership, args={}):
+    def make_membership_event(self, destination, room_id, user_id, membership):
         valid_memberships = {Membership.JOIN, Membership.LEAVE}
         if membership not in valid_memberships:
             raise RuntimeError(
@@ -173,7 +173,6 @@ class TransportLayerClient(object):
         content = yield self.client.get_json(
             destination=destination,
             path=path,
-            args=args,
             retry_on_dns_fail=True,
         )
 
@@ -218,6 +217,19 @@ class TransportLayerClient(object):
 
         defer.returnValue(response)
 
+    @defer.inlineCallbacks
+    @log_function
+    def exchange_third_party_invite(self, destination, room_id, event_dict):
+        path = PREFIX + "/exchange_third_party_invite/%s" % (room_id,)
+
+        response = yield self.client.put_json(
+            destination=destination,
+            path=path,
+            data=event_dict,
+        )
+
+        defer.returnValue(response)
+
     @defer.inlineCallbacks
     @log_function
     def get_event_auth(self, destination, room_id, event_id):

synapse/federation/transport/server.py

@@ -292,7 +292,7 @@ class FederationMakeJoinServlet(BaseFederationServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, origin, content, query, context, user_id):
-        content = yield self.handler.on_make_join_request(context, user_id, query)
+        content = yield self.handler.on_make_join_request(context, user_id)
         defer.returnValue((200, content))
 
 
@@ -343,6 +343,17 @@ class FederationInviteServlet(BaseFederationServlet):
         defer.returnValue((200, content))
 
 
+class FederationThirdPartyInviteExchangeServlet(BaseFederationServlet):
+    PATH = "/exchange_third_party_invite/([^/]*)"
+
+    @defer.inlineCallbacks
+    def on_PUT(self, origin, content, query, room_id):
+        content = yield self.handler.on_exchange_third_party_invite_request(
+            origin, room_id, content
+        )
+        defer.returnValue((200, content))
+
+
 class FederationClientKeysQueryServlet(BaseFederationServlet):
     PATH = "/user/keys/query"
 
@@ -396,6 +407,30 @@ class FederationGetMissingEventsServlet(BaseFederationServlet):
         defer.returnValue((200, content))
 
 
+class On3pidBindServlet(BaseFederationServlet):
+    PATH = "/3pid/onbind"
+
+    @defer.inlineCallbacks
+    def on_POST(self, request):
+        content_bytes = request.content.read()
+        content = json.loads(content_bytes)
+        if "invites" in content:
+            last_exception = None
+            for invite in content["invites"]:
+                try:
+                    yield self.handler.exchange_third_party_invite(invite)
+                except Exception as e:
+                    last_exception = e
+            if last_exception:
+                raise last_exception
+        defer.returnValue((200, {}))
+
+    # Avoid doing remote HS authorization checks which are done by default by
+    # BaseFederationServlet.
+    def _wrap(self, code):
+        return code
+
+
 SERVLET_CLASSES = (
     FederationPullServlet,
     FederationEventServlet,
@@ -413,4 +448,6 @@ SERVLET_CLASSES = (
     FederationEventAuthServlet,
     FederationClientKeysQueryServlet,
     FederationClientKeysClaimServlet,
+    FederationThirdPartyInviteExchangeServlet,
+    On3pidBindServlet,
 )

synapse/handlers/_base.py

@@ -21,7 +21,6 @@ from synapse.api.constants import Membership, EventTypes
 from synapse.types import UserID, RoomAlias
 
 from synapse.util.logcontext import PreserveLoggingContext
-from synapse.util import third_party_invites
 
 import logging
 
@@ -192,16 +191,6 @@ class BaseHandler(object):
                         )
                     )
 
-        if (
-            event.type == EventTypes.Member and
-            event.content["membership"] == Membership.JOIN and
-            third_party_invites.join_has_third_party_invite(event.content)
-        ):
-            yield third_party_invites.check_key_valid(
-                self.hs.get_simple_http_client(),
-                event
-            )
-
         federation_handler = self.hs.get_handlers().federation_handler
 
         if event.type == EventTypes.Member:

synapse/handlers/federation.py

@@ -21,6 +21,7 @@ from synapse.api.errors import (
     AuthError, FederationError, StoreError, CodeMessageException, SynapseError,
 )
 from synapse.api.constants import EventTypes, Membership, RejectedReason
+from synapse.events.validator import EventValidator
 from synapse.util import unwrapFirstError
 from synapse.util.logcontext import PreserveLoggingContext
 from synapse.util.logutils import log_function
@@ -39,7 +40,6 @@ from twisted.internet import defer
 
 import itertools
 import logging
-from synapse.util import third_party_invites
 
 logger = logging.getLogger(__name__)
 
@@ -58,6 +58,8 @@ class FederationHandler(BaseHandler):
     def __init__(self, hs):
         super(FederationHandler, self).__init__(hs)
 
+        self.hs = hs
+
         self.distributor.observe(
             "user_joined_room",
             self._on_user_joined
@@ -68,7 +70,6 @@ class FederationHandler(BaseHandler):
         self.store = hs.get_datastore()
         self.replication_layer = hs.get_replication_layer()
         self.state_handler = hs.get_state_handler()
-        # self.auth_handler = gs.get_auth_handler()
         self.server_name = hs.hostname
         self.keyring = hs.get_keyring()
 
@@ -563,7 +564,7 @@ class FederationHandler(BaseHandler):
 
     @log_function
     @defer.inlineCallbacks
-    def do_invite_join(self, target_hosts, room_id, joinee, content):
+    def do_invite_join(self, target_hosts, room_id, joinee):
         """ Attempts to join the `joinee` to the room `room_id` via the
         server `target_host`.
 
@@ -583,8 +584,7 @@ class FederationHandler(BaseHandler):
             target_hosts,
             room_id,
             joinee,
-            "join",
+            "join"
-            content
         )
 
         self.room_queues[room_id] = []
@@ -661,16 +661,12 @@ class FederationHandler(BaseHandler):
 
     @defer.inlineCallbacks
     @log_function
-    def on_make_join_request(self, room_id, user_id, query):
+    def on_make_join_request(self, room_id, user_id):
         """ We've received a /make_join/ request, so we create a partial
         join event for the room and return that. We do *not* persist or
         process it until the other server has signed it and sent it back.
         """
         event_content = {"membership": Membership.JOIN}
-        if third_party_invites.has_join_keys(query):
-            event_content["third_party_invite"] = (
-                third_party_invites.extract_join_keys(query)
-            )
 
         builder = self.event_builder_factory.new({
             "type": EventTypes.Member,
@@ -686,9 +682,6 @@ class FederationHandler(BaseHandler):
 
         self.auth.check(event, auth_events=context.current_state)
 
-        if third_party_invites.join_has_third_party_invite(event.content):
-            third_party_invites.check_key_valid(self.hs.get_simple_http_client(), event)
-
         defer.returnValue(event)
 
     @defer.inlineCallbacks
@@ -828,8 +821,7 @@ class FederationHandler(BaseHandler):
             target_hosts,
             room_id,
             user_id,
-            "leave",
+            "leave"
-            {}
         )
         signed_event = self._sign_event(event)
 
@@ -848,13 +840,12 @@ class FederationHandler(BaseHandler):
         defer.returnValue(None)
 
     @defer.inlineCallbacks
-    def _make_and_verify_event(self, target_hosts, room_id, user_id, membership, content):
+    def _make_and_verify_event(self, target_hosts, room_id, user_id, membership):
         origin, pdu = yield self.replication_layer.make_membership_event(
             target_hosts,
             room_id,
             user_id,
-            membership,
+            membership
-            content
         )
 
         logger.debug("Got response to make_%s: %s", membership, pdu)
@@ -1647,3 +1638,75 @@ class FederationHandler(BaseHandler):
             },
             "missing": [e.event_id for e in missing_locals],
         })
+
+    @defer.inlineCallbacks
+    @log_function
+    def exchange_third_party_invite(self, invite):
+        sender = invite["sender"]
+        room_id = invite["room_id"]
+
+        event_dict = {
+            "type": EventTypes.Member,
+            "content": {
+                "membership": Membership.INVITE,
+                "third_party_invite": invite,
+            },
+            "room_id": room_id,
+            "sender": sender,
+            "state_key": invite["mxid"],
+        }
+
+        if (yield self.auth.check_host_in_room(room_id, self.hs.hostname)):
+            builder = self.event_builder_factory.new(event_dict)
+            EventValidator().validate_new(builder)
+            event, context = yield self._create_new_client_event(builder=builder)
+            self.auth.check(event, context.current_state)
+            yield self._validate_keyserver(event, auth_events=context.current_state)
+            member_handler = self.hs.get_handlers().room_member_handler
+            yield member_handler.change_membership(event, context)
+        else:
+            destinations = set([x.split(":", 1)[-1] for x in (sender, room_id)])
+            yield self.replication_layer.forward_third_party_invite(
+                destinations,
+                room_id,
+                event_dict,
+            )
+
+    @defer.inlineCallbacks
+    @log_function
+    def on_exchange_third_party_invite_request(self, origin, room_id, event_dict):
+        builder = self.event_builder_factory.new(event_dict)
+
+        event, context = yield self._create_new_client_event(
+            builder=builder,
+        )
+
+        self.auth.check(event, auth_events=context.current_state)
+        yield self._validate_keyserver(event, auth_events=context.current_state)
+
+        returned_invite = yield self.send_invite(origin, event)
+        # TODO: Make sure the signatures actually are correct.
+        event.signatures.update(returned_invite.signatures)
+        member_handler = self.hs.get_handlers().room_member_handler
+        yield member_handler.change_membership(event, context)
+
+    @defer.inlineCallbacks
+    def _validate_keyserver(self, event, auth_events):
+        token = event.content["third_party_invite"]["signed"]["token"]
+
+        invite_event = auth_events.get(
+            (EventTypes.ThirdPartyInvite, token,)
+        )
+
+        try:
+            response = yield self.hs.get_simple_http_client().get_json(
+                invite_event.content["key_validity_url"],
+                {"public_key": invite_event.content["public_key"]}
+            )
+        except Exception:
+            raise SynapseError(
+                502,
+                "Third party certificate could not be checked"
+            )
+        if "valid" not in response or not response["valid"]:
+            raise AuthError(403, "Third party certificate was invalid")

synapse/handlers/room.py

@@ -38,6 +38,8 @@ import string
 
 logger = logging.getLogger(__name__)
 
+id_server_scheme = "https://"
+
 
 class RoomCreationHandler(BaseHandler):
 
@@ -488,8 +490,7 @@ class RoomMemberHandler(BaseHandler):
             yield handler.do_invite_join(
                 room_hosts,
                 room_id,
-                event.user_id,
+                event.user_id
-                event.content  # FIXME To get a non-frozen dict
             )
         else:
             logger.debug("Doing normal join")
@@ -632,7 +633,7 @@ class RoomMemberHandler(BaseHandler):
         """
         try:
             data = yield self.hs.get_simple_http_client().get_json(
-                "https://%s/_matrix/identity/api/v1/lookup" % (id_server,),
+                "%s%s/_matrix/identity/api/v1/lookup" % (id_server_scheme, id_server,),
                 {
                     "medium": medium,
                     "address": address,
@@ -655,8 +656,8 @@ class RoomMemberHandler(BaseHandler):
             raise AuthError(401, "No signature from server %s" % (server_hostname,))
         for key_name, signature in data["signatures"][server_hostname].items():
             key_data = yield self.hs.get_simple_http_client().get_json(
-                "https://%s/_matrix/identity/api/v1/pubkey/%s" %
+                "%s%s/_matrix/identity/api/v1/pubkey/%s" %
-                (server_hostname, key_name,),
+                (id_server_scheme, server_hostname, key_name,),
             )
             if "public_key" not in key_data:
                 raise AuthError(401, "No public key named %s from %s" %
@@ -709,7 +710,9 @@ class RoomMemberHandler(BaseHandler):
     @defer.inlineCallbacks
     def _ask_id_server_for_third_party_invite(
             self, id_server, medium, address, room_id, sender):
-        is_url = "https://%s/_matrix/identity/api/v1/store-invite" % (id_server,)
+        is_url = "%s%s/_matrix/identity/api/v1/store-invite" % (
+            id_server_scheme, id_server,
+        )
         data = yield self.hs.get_simple_http_client().post_urlencoded_get_json(
             is_url,
             {
@@ -722,8 +725,8 @@ class RoomMemberHandler(BaseHandler):
         # TODO: Check for success
         token = data["token"]
         public_key = data["public_key"]
-        key_validity_url = "https://%s/_matrix/identity/api/v1/pubkey/isvalid" % (
+        key_validity_url = "%s%s/_matrix/identity/api/v1/pubkey/isvalid" % (
-            id_server,
+            id_server_scheme, id_server,
         )
         defer.returnValue((token, public_key, key_validity_url))
 

synapse/rest/client/v1/room.py

@@ -26,7 +26,6 @@ from synapse.events.utils import serialize_event
 import simplejson as json
 import logging
 import urllib
-from synapse.util import third_party_invites
 
 logger = logging.getLogger(__name__)
 
@@ -453,7 +452,7 @@ class RoomMembershipRestServlet(ClientV1RestServlet):
         # target user is you unless it is an invite
         state_key = user.to_string()
 
-        if membership_action == "invite" and third_party_invites.has_invite_keys(content):
+        if membership_action == "invite" and self._has_3pid_invite_keys(content):
             yield self.handlers.room_member_handler.do_3pid_invite(
                 room_id,
                 user,
@@ -480,19 +479,10 @@ class RoomMembershipRestServlet(ClientV1RestServlet):
 
         msg_handler = self.handlers.message_handler
 
-        event_content = {
-            "membership": unicode(membership_action),
-        }
-
-        if membership_action == "join" and third_party_invites.has_join_keys(content):
-            event_content["third_party_invite"] = (
-                third_party_invites.extract_join_keys(content)
-            )
-
         yield msg_handler.create_and_send_event(
             {
                 "type": EventTypes.Member,
-                "content": event_content,
+                "content": {"membership": unicode(membership_action)},
                 "room_id": room_id,
                 "sender": user.to_string(),
                 "state_key": state_key,
@@ -503,6 +493,12 @@ class RoomMembershipRestServlet(ClientV1RestServlet):
 
         defer.returnValue((200, {}))
 
+    def _has_3pid_invite_keys(self, content):
+        for key in {"id_server", "medium", "address", "display_name"}:
+            if key not in content:
+                return False
+        return True
+
     @defer.inlineCallbacks
     def on_PUT(self, request, room_id, membership_action, txn_id):
         try:

synapse/util/third_party_invites.py

@@ -1,69 +0,0 @@
-# -*- coding: utf-8 -*-
-# Copyright 2015 OpenMarket Ltd
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-from twisted.internet import defer
-from synapse.api.errors import AuthError
-
-
-INVITE_KEYS = {"id_server", "medium", "address", "display_name"}
-
-JOIN_KEYS = {
-    "token",
-    "public_key",
-    "key_validity_url",
-    "sender",
-    "signed",
-}
-
-
-def has_invite_keys(content):
-    for key in INVITE_KEYS:
-        if key not in content:
-            return False
-    return True
-
-
-def has_join_keys(content):
-    for key in JOIN_KEYS:
-        if key not in content:
-            return False
-    return True
-
-
-def join_has_third_party_invite(content):
-    if "third_party_invite" not in content:
-        return False
-    return has_join_keys(content["third_party_invite"])
-
-
-def extract_join_keys(src):
-    return {
-        key: value
-        for key, value in src.items()
-        if key in JOIN_KEYS
-    }
-
-
-@defer.inlineCallbacks
-def check_key_valid(http_client, event):
-    try:
-        response = yield http_client.get_json(
-            event.content["third_party_invite"]["key_validity_url"],
-            {"public_key": event.content["third_party_invite"]["public_key"]}
-        )
-    except Exception:
-        raise AuthError(502, "Third party certificate could not be checked")
-    if "valid" not in response or not response["valid"]:
-        raise AuthError(403, "Third party certificate was invalid")