code: def _refresh(self, _):
          
          # pylint: disable=import-error
          from google.appengine.api import app_identity
          try:
              token, _ = app_identity.get_access_token(self._scopes)
          except app_identity.Error as e:
              raise exceptions.CredentialsError(str(e))
          self.access_token = token
docs: Refresh self.access_token.
  
          Args:
            _: (ignored) A function matching httplib2.Http.request's signature.