code: def ensure_signed_credentials(credentials):
      
      if not isinstance(credentials, google.auth.credentials.Signing):
          auth_uri = (
              "https://google-cloud-python.readthedocs.io/en/latest/"
              "core/auth.html?highlight=authentication#setting-up-"
              "a-service-account"
          )
          raise AttributeError(
              "you need a private key to sign credentials."
              "the credentials you are currently using %s "
              "just contains a token. see %s for more "
              "details." % (type(credentials), auth_uri)
          )
docs: Raise AttributeError if the credentials are unsigned.
  
      :type credentials: :class:`google.auth.credentials.Signing`
      :param credentials: The credentials used to create a private key
                          for signing text.
  
      :raises: :exc:`AttributeError` if credentials is not an instance
              of :class:`google.auth.credentials.Signing`.