1. Introduction

Goal of the Tutorial

This tutorial aims to introduce you to the concepts of Identity Federation and Single Sign-On (SSO). These are authentication techniques that allow users to use a single set of credentials to log into multiple applications.

What You Will Learn

By the end of this tutorial, you'll have a solid understanding of Identity Federation and Single Sign-On. You'll learn how they work, why they are important, and how to implement them.

Prerequisites

Basic understanding of web development and authentication mechanisms is recommended but not mandatory. Familiarity with JavaScript can be helpful for the code examples.

2. Step-by-Step Guide

Identity Federation

Identity Federation is a system of trust between various software applications across multiple enterprises. It allows a user's roles, identities, and attributes to be trusted across these applications.

For example, consider two organizations, A and B. If a user is authenticated in organization A, then organization B can trust this authentication and allow the user to access its resources without needing to re-authenticate.

Single Sign-On (SSO)

Single Sign-On (SSO) is an authentication service that allows a user to use one set of login credentials (e.g., name and password) to access multiple applications. The service authenticates the user for all the applications they have been given rights to and eliminates further prompts when the user switches applications during the same session.

For example, Google uses SSO for their services. Once you log into Gmail, you can access YouTube, Google Drive, and more, without needing to log in again.

3. Code Examples

Below is a simple example of how to set up SSO using JavaScript and the Passport.js library.

// Import needed modules
const express = require('express');
const passport = require('passport');
const GoogleStrategy = require('passport-google-oauth20').Strategy;

// Initialize express app
const app = express();

// Use session cookies with passport
app.use(passport.initialize());
app.use(passport.session());

// Configure passport with Google's OAuth 2.0 strategy
passport.use(new GoogleStrategy({
    clientID: GOOGLE_CLIENT_ID,
    clientSecret: GOOGLE_CLIENT_SECRET,
    callbackURL: "http://yourwebsite.com/auth/google/callback"
  },
  function(accessToken, refreshToken, profile, cb) {
    // In a real app, you'd typically look up the user in your database here
    // For this example, we're just passing Google's profile info on to the callback
    return cb(null, profile);
  }
));

// Route for logging in with Google
app.get('/auth/google',
  passport.authenticate('google', { scope: ['profile', 'email'] }));

// Route for Google authentication callback
// On success, redirect to the home page
// On failure, redirect to login page
app.get('/auth/google/callback',
  passport.authenticate('google', { failureRedirect: '/login' }),
  function(req, res) {
    res.redirect('/');
  });

// Start the server
app.listen(3000);

This code creates an Express.js server and uses Passport.js with Google's OAuth 2.0 strategy for SSO. The user's Google profile information is used as their identity.

4. Summary

In this tutorial, we introduced the concepts of Identity Federation and SSO. We learned that Identity Federation allows user identities to be trusted across different applications, and SSO allows users to log into multiple applications with a single set of credentials. We also looked at a simple SSO example using JavaScript and Passport.js.

Next, you could extend your knowledge by exploring other authentication strategies with Passport.js, or by implementing SSO in a full-stack application.

Some additional resources on these topics include:

• Passport.js Documentation
• OAuth 2.0 Protocol
• Google's OAuth 2.0 Playground

5. Practice Exercises

1. Implement SSO with Facebook using Passport.js.
2. Tip: Look for Passport's Facebook strategy.

3. Solution: Similar to the Google example above, but use passport-facebook strategy instead.

4. Implement SSO in a full-stack application, using any front-end and back-end frameworks you prefer.

5. Tip: You'll need to handle the authenticated user's identity on both the client and server.

6. Solution: This will depend on the technologies you chose, but the general idea is to authenticate on the server, then send some indication of the user's identity (like a JWT) to the client.

7. Implement an Identity Federation system between two separate applications.

8. Tip: You'll need to set up a trusted relationship between the two applications.
9. Solution: This will depend heavily on the specifics of the applications, but in general, you'll need to establish trust by sharing some secret (like an API key) and use that to verify requests from one app to the other.