code: def handle_authorized_event(self, event):
          
          self.server = event.authorized_jid.bare()
          if "versioning" in self.server_features:
              if self.roster is not None and self.roster.version is not None:
                  version = self.roster.version
              else:
                  version = u""
          else:
              version = None
          self.request_roster(version)
docs: Request roster upon login.