code: def locked_put(self, credentials):
          
          entity = self._model.get_or_insert(self._key_name)
          setattr(entity, self._property_name, credentials)
          entity.put()
          if self._cache:
              self._cache.set(self._key_name, credentials.to_json())
docs: Write a Credentials to the datastore.
  
          Args:
              credentials: Credentials, the credentials to store.