'Check that the provided token belongs to the user.
:param context: standard context
:param user_id: id of user
:raises keystone.exception.Forbidden: when token is invalid'

def _assert_identity(self, context, user_id):

    token_ref = authorization.get_token_ref(context)
    if (token_ref.user_id != user_id):
        raise exception.Forbidden(_('Token    belongs    to    another    user'))
