An example of using Douglas Crockford's JavaScript Sealer/Unsealer method for securely authenticating users. http://www.yuiblog.com/blog/2010/02/24/video-crockonjs-3/

passwordSealer.js

var makeSealer = function () {
    var users = [], passwords = [];

    return {
        sealer: function (username, password) {
            var i = users.length,
                user = {username: username};
            users[i] = user;
            passwords[i] = password;
            return user;
        },
        unsealer: function (user, password) {
            return passwords[users.indexOf(user)] === password;
        }
    };
}

// Testing code.
var testUnsealer = function () {
    var testUnsealerValue = function (user, password, value, id) {
        console.log(ms.unsealer(user, password) === value ? "Test " + id + " passed." : "Test " + id + " failed.");
    };
    
    var ms = makeSealer();
    var adminUser = ms.sealer("Admin", "MyAdminPassword");
    
    testUnsealerValue(adminUser, "MyAdminPassw0rd", false, 1);
    testUnsealerValue(adminUser, "MyAdminPassword", true, 2);
};