    credentials = jwt.Credentials.from_service_account_file(
            'service-account.json',
            audience=audience,
            additional_claims={'meta': 'data'})

    You can also construct the credentials directly if you have a
    :class:`~google.auth.crypt.Signer` instance::

        credentials = jwt.Credentials(
            signer,
            issuer='your-issuer',
            subject='your-subject',
            audience=audience)

    The claims are considered immutable. If you want to modify the claims,
    you can easily create another instance using :meth:`with_claims`::

        new_audience = (
            'https://pubsub.googleapis.com/google.pubsub.v1.Subscriber')
        new_credentials = credentials.with_claims(audience=new_audience)
    Nc