How to use Passport.js in Express app

Using Passport.js in an Express application allows you to implement various authentication strategies with ease. Passport is a popular middleware for authentication in Node.js applications and supports a variety of strategies for authenticating requests.

Step-by-Step Guide to Using Passport in Express

1. Install Necessary Packages:

   Install passport, passport-local, express-session, and body-parser (if not already installed):

   npm install express passport passport-local express-session body-parser
   

2. Set Up Express Application:

   Create a basic Express application and configure Passport:

   const express = require('express');
   const session = require('express-session');
   const passport = require('passport');
   const LocalStrategy = require('passport-local').Strategy;
   const bodyParser = require('body-parser');
   
   const app = express();
   
   // Use body-parser middleware
   app.use(bodyParser.urlencoded({ extended: false }));
   
   // Set up session middleware
   app.use(session({
       secret: 'your-secret-key', // Replace with your secret key
       resave: false,
       saveUninitialized: false
   }));
   
   // Initialize Passport and use it with session
   app.use(passport.initialize());
   app.use(passport.session());
   
   // Example users database
   const users = [
       { id: 1, username: 'test', password: 'password' }
   ];
   
   // Configure Passport Local Strategy
   passport.use(new LocalStrategy(
       function(username, password, done) {
           const user = users.find(u => u.username === username);
           if (!user) {
               return done(null, false, { message: 'Incorrect username.' });
           }
           if (user.password !== password) {
               return done(null, false, { message: 'Incorrect password.' });
           }
           return done(null, user);
       }
   ));
   
   // Serialize user to store user ID in session
   passport.serializeUser(function(user, done) {
       done(null, user.id);
   });
   
   // Deserialize user by ID stored in session
   passport.deserializeUser(function(id, done) {
       const user = users.find(u => u.id === id);
       done(null, user);
   });
   
   // Route to display login form
   app.get('/login', (req, res) => {
       res.send(`
           <form action="/login" method="post">
               <div>
                   <label>Username:</label>
                   <input type="text" name="username"/>
               </div>
               <div>
                   <label>Password:</label>
                   <input type="password" name="password"/>
               </div>
               <div>
                   <button type="submit">Log In</button>
               </div>
           </form>
       `);
   });
   
   // Route to handle login form submission
   app.post('/login',
       passport.authenticate('local', {
           successRedirect: '/profile',
           failureRedirect: '/login',
           failureFlash: false
       })
   );
   
   // Route to display profile if authenticated
   app.get('/profile', (req, res) => {
       if (!req.isAuthenticated()) {
           return res.redirect('/login');
       }
       res.send(`Hello ${req.user.username}, you are authenticated!`);
   });
   
   // Start the server
   const PORT = process.env.PORT || 3000;
   app.listen(PORT, () => {
       console.log(`Server is running on http://localhost:${PORT}`);
   });
   

3. Explanation:

   • Session Middleware: Configures session handling with express-session.
   • Passport Middleware: Initializes Passport and configures it to use sessions.
   • User Database: A simple array of users for demonstration purposes.
   • LocalStrategy: Configures Passport to use the local strategy for authentication.
     • The LocalStrategy function checks if the username and password match a user in the array.
   • Serialization and Deserialization: Handles storing user information in the session and retrieving it.
   • Login Route: Displays a simple login form.
   • Login Form Handling: Authenticates user credentials using passport.authenticate().
   • Profile Route: Displays the user profile if authenticated.