code: def _refresh(self, http):
          
          try:
              scopes = self.scope.split()
              (token, _) = app_identity.get_access_token(
                  scopes, service_account_id=self.service_account_id)
          except app_identity.Error as e:
              raise client.AccessTokenRefreshError(str(e))
          self.access_token = token
docs: Refreshes the access token.
  
          Since the underlying App Engine app_identity implementation does its
          own caching we can skip all the storage hoops and just to a refresh
          using the API.
  
          Args:
              http: unused HTTP object
  
          Raises:
              AccessTokenRefreshError: When the refresh fails.