app.post("/api/register", function(req, res) {

    var user = User.build({
        userName: req.body.username,
        email: req.body.email,
        password: req.body.password,
        gameData: "{currentLevel:0}"

    });

    req.session.user = user; // creates session and works!
    // Now how to get it stored on client browser ?????

    user.save();

});

$.post("http://localhost:3000/api/register", {
        username: $username,
        email: $email,
        password: $password
    }).done(function(data) {

         // get session and store on users browser

    });