def add_code_verifier(request_args, service, **kwargs):
    """
    PKCE RFC 7636 support
    To be added as a post_construct method to an
    :py:class:`oidcservice.oidc.service.AccessToken` instance

    :param service: The service that uses this function
    :param request_args: Set of request arguments
    :return: updated set of request arguments
    """
    _item = service.get_item(Message, 'pkce', kwargs['state'])
    request_args.update({'code_verifier': _item['code_verifier']})
    return request_args