2 files changed, 31 insertions, 0 deletions
diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index 3beab47832..370f7ba78b 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -615,6 +615,19 @@ class TransportLayerClient(object):
         )
 
     @log_function
+    def join_group(self, destination, group_id, user_id, content):
+        """Attempts to join a group
+        """
+        path = PREFIX + "/groups/%s/users/%s/join" % (group_id, user_id)
+
+        return self.client.post_json(
+            destination=destination,
+            path=path,
+            data=content,
+            ignore_backoff=True,
+        )
+
+    @log_function
     def invite_to_group(self, destination, group_id, user_id, requester_user_id, content):
         """Invite a user to a group
         """
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index b98e30459c..4c94d5a36c 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -803,6 +803,23 @@ class FederationGroupsAcceptInviteServlet(BaseFederationServlet):
         defer.returnValue((200, new_content))
 
 
+class FederationGroupsJoinServlet(BaseFederationServlet):
+    """Attempt to join a group
+    """
+    PATH = "/groups/(?P<group_id>[^/]*)/users/(?P<user_id>[^/]*)/join$"
+
+    @defer.inlineCallbacks
+    def on_POST(self, origin, content, query, group_id, user_id):
+        if get_domain_from_id(user_id) != origin:
+            raise SynapseError(403, "user_id doesn't match origin")
+
+        new_content = yield self.handler.join_group(
+            group_id, user_id, content,
+        )
+
+        defer.returnValue((200, new_content))
+
+
 class FederationGroupsRemoveUserServlet(BaseFederationServlet):
     """Leave or kick a user from the group
     """
@@ -1182,6 +1199,7 @@ GROUP_SERVER_SERVLET_CLASSES = (
     FederationGroupsInvitedUsersServlet,
     FederationGroupsInviteServlet,
     FederationGroupsAcceptInviteServlet,
+    FederationGroupsJoinServlet,
     FederationGroupsRemoveUserServlet,
     FederationGroupsSummaryRoomsServlet,
     FederationGroupsCategoriesServlet,