app.config(function(RestangularProvider) {

    // add a response intereceptor
    RestangularProvider.addResponseInterceptor(function(data, operation, what, url, response, deferred) {
    // check the response if it contains error or not.
      if (typeof(response.error) !== 'undefined') {
            alert('Your authentication Fail!');
            return false;
        };
      return response;
    });

});