Make sure there is an active span here.

synapse/api/auth.py

@@ -179,6 +179,7 @@ class Auth(object):
     def get_public_keys(self, invite_event):
         return event_auth.get_public_keys(invite_event)
 
+    @opentracing.trace_deferred
     @defer.inlineCallbacks
     def get_user_by_req(
         self, request, allow_guest=False, rights="access", allow_expired=False