So I have my Grails environment setup. The point is to build a REST-service that will work as a back end to a highly dynamic JavaScript page. I chose Grails, since it builds on Hibernate and Spring.

Two frameworks Id like to examine for the purpose of seeing the differences between Castle and nHibernate in the .Net world.

Building domain-classes and having the represented as XML is straight forward in Grails, but I need to take care of the login scenario. If you’d like to know more about building REST web services with Grails, I recommend reading the Mastering Grails: RESTful Grails article. Login seems like a good place to start, to ensure that my domain-controllers can dictate login as I develop the domain.

Now Grails.org has a list of tutorials, one of them, focusing on Login. It’s a good beginners tutorial showing how to use interceptors to execute user verification before showing the actual view requested. For my scenario however it has a few problems. Lets use the tutorial as a start of point.

The problems I have with the solution is with the following code:

def checkUser() {
  if(!session.user) {
    // i.e. user not logged in
    redirect(controller:'user',action:'login')
    return false
  }
}

For my scenario this has one problem, in two places. Its stateful. First of it always directs the user to the same place, of course it can be different per controller. I need it to simple say access denied.

def checkUser() {
  if(!session.user) {
    // i.e. user not logged in
    response.sendError(401)
    return false
  }
}

The above code is changed to instead of redirecting the user, it simply sets the response code to Access Denied. Now there’s just one issue left, the session code.

I don’t want to use session, as it requires my server to remember each session, preferably I want the client to remember the state.

Another issue is that I want to use Mor.ph AppSpace, if I pay for the most basic of subscriptions at Mor.ph I get two Cube, i.e. two servers with a load balancers in front. As a result I can’t be sure that the same server will service the same client all the time.

If we instead choose to check for the logged in user using the authorization header. The state is always provided by the client, instead of keeping the state on the server.

def checkUser() {
  if(!UserController.checkAuthorization(request, response)) {
    // i.e. user not logged in
    response.sendError(401)
    return false
  }
  return true
}

I let the UserController do the checking of the user, using a static method. This will let me keep the authorization code in the same place I handle users to begin with. It also allows me to change the authorization method later by changing the code in the checkAuthorization method. We could use Dependency Injection here to inject a real instance of the UserController, or even better an object with the sole responsibility to check user access. However DI is out of scope for this post.

You can implement any way of checking the user login you want. If you want a simple solution and stick with the HTTP standard you could use Basic auth. Here is a good explaination of how to implement Basic auth for Grails. Another way is too use a cookie to hold authorization information.

For this example were just sending username:password in the authorization header. My final implementation will be Basic Auth with the password hashed to a checksum. The point of the hash is to never send plain-text password across the net.

Here is the checkAuthorization method in the UserController for this example.

static boolean checkAuthorization(HttpServletRequest request, HttpServletResponse response) {
  def authString = request.getHeader('Authorization')

  if (!authString) {
    return false;
  }

  def credentials = authString.split(':')
  if( credentials.length != 2 || credentials[0] == null || credentials[0] == "" || credentials[1] == "" || credentials[1] == null)
    return false;

  def user = User.findByEmailAndPassword(credentials[0], credentials[1])

  if (user) {
    return true;
  }
  return false;
}

Now we can create some JQuery based JavaScript code to handle login.

function RestClient() {
    var self = this;
    var auth;

    function ShowLoginUI(afterLoginCallback) {
        var dialog = document.createElement('div');
        $(dialog).html("<table><tr><td>Email</td><td><input id='email' type='text'/></td></tr><tr><td>Password</td><td><input id='pass' type='password'/></td></tr></table>");
        $(dialog).dialog({ buttons: {"Login": function() {
            auth = $(this).find("#email").val() + ":" + $(this).find("#pass").val();
            afterLoginCallback();
            $(this).dialog("close");
        }, "Cancel":function() {
            $(this).dialog("close");
        }}, modal:true});
    }

    this.Get = function(url) {
        var data = null;

        data = $.ajax({
            url : url,
            method : 'GET',
            beforeSend : function(req) {
                req.setRequestHeader('Authorization', auth);
            }, cache : true,
            error: function(request, textStatus, error) {
                if (request.status == 401) {
                    ShowLoginUI(function() {
                        data = self.Get(url);
                    });
                }
            }});

        return data;
    };
}

The above code does Ajax Get-calls to the specified address. If the call failed due to Access Denied, it shows a login form and tries to execute the Ajax request again. The class remembers the authorization string, so as long as the user uses the same RestClient-object the state is maintained at the client side.
Ill leave instructions on how to wire up Grails with JQuery to someone else.

Here is a simple usage example:

var a = new RestClient();
$("#test").click(function() {
  var data = a.Get("plant/create");
  $(document).append(data);
});

Good luck writing scalable login scenarios using Ajax instead of page reloads.