'Send credentials to server.
:param scheme: authentication scheme (default supported:
"digest").
:param credential: the credential -- value depends on scheme.
:returns: True if it was successful.
:rtype: bool
:raises:
:exc:`~kazoo.exceptions.AuthFailedError` if it failed though
the session state will be set to AUTH_FAILED as well.'

def add_auth(self, scheme, credential):

    return self.add_auth_async(scheme, credential).get()
