Session-based auth with express-session

Introduction

Session-based authentication helps keep users logged in by remembering them on the server. It stores user info safely between requests.

You want users to log in and stay logged in while using your website.

You need to protect pages so only logged-in users can see them.

You want to keep track of user data without asking them to log in every time.

You want a simple way to manage user sessions without tokens.

You want to store user info securely on the server side.

Syntax

Express

const session = require('express-session');

app.use(session({
  secret: 'your-secret-key',
  resave: false,
  saveUninitialized: false,
  cookie: { secure: false }
}));

secret is a string used to sign the session ID cookie. Keep it safe.

resave false means don't save session if nothing changed.

Examples

This sets up sessions with a secret and saves new sessions even if empty.

Express

app.use(session({
  secret: 'keyboard cat',
  resave: false,
  saveUninitialized: true
}));

This configures the cookie to be sent only over HTTPS (secure).

Express

app.use(session({
  secret: 'mySecret',
  cookie: { secure: true }
}));

Sample Program

This example shows a simple Express app using express-session to handle login, protect a dashboard page, and logout. User info is stored in the session.

Express

const express = require('express');
const session = require('express-session');

const app = express();
app.use(express.urlencoded({ extended: true }));

app.use(session({
  secret: 'simpleSecret',
  resave: false,
  saveUninitialized: false,
  cookie: { secure: false }
}));

// Simple user database
const users = { user1: 'pass1', user2: 'pass2' };

// Login form
app.get('/login', (req, res) => {
  res.send(`<form method='POST' action='/login'>
    <input name='username' placeholder='Username' required />
    <input name='password' type='password' placeholder='Password' required />
    <button type='submit'>Login</button>
  </form>`);
});

// Handle login
app.post('/login', (req, res) => {
  const { username, password } = req.body;
  if (users[username] && users[username] === password) {
    req.session.user = username;
    res.send(`Welcome, ${username}! <a href='/dashboard'>Go to Dashboard</a>`);
  } else {
    res.send('Invalid login. <a href="/login">Try again</a>');
  }
});

// Protected dashboard
app.get('/dashboard', (req, res) => {
  if (req.session.user) {
    res.send(`Hello ${req.session.user}, this is your dashboard. <a href='/logout'>Logout</a>`);
  } else {
    res.send('Please <a href="/login">login</a> first.');
  }
});

// Logout
app.get('/logout', (req, res) => {
  req.session.destroy(err => {
    if (err) {
      return res.send('Error logging out');
    }
    res.send('Logged out. <a href="/login">Login again</a>');
  });
});

app.listen(3000, () => console.log('Server running on http://localhost:3000'));

Important Notes

Always keep your session secret private and strong.

Set cookie.secure to true only if your site uses HTTPS.

Sessions store data on the server, so they are safer than storing info in cookies.

Summary

Session-based auth keeps users logged in by storing info on the server.

Use express-session middleware to manage sessions easily.

Protect routes by checking if session user info exists.

Practice

1. What is the main purpose of using express-session in an Express app?

easy

A. To store user data on the server and keep users logged in across requests

B. To encrypt user passwords before saving to the database

C. To serve static files like images and CSS

D. To handle HTTP request routing

Solution

1. Step 1: Understand session purpose

   Sessions store user info on the server to remember users between requests.

2. Step 2: Identify express-session role

   The express-session middleware manages these sessions automatically.

3. Final Answer:

   To store user data on the server and keep users logged in across requests -> Option A

4. Quick Check:

   Session-based auth = store user data server-side [OK]

Hint: Sessions keep user info server-side to maintain login [OK]

Common Mistakes:

• Confusing sessions with password encryption
• Thinking sessions serve static files
• Mixing routing with session management

2. Which of the following is the correct way to initialize express-session middleware in an Express app?

easy

A. app.use(expressSession('keyboard cat'))

B. app.session({ secret: 'keyboard cat', resave: true })

C. app.use(session({ secret: 'keyboard cat', resave: false, saveUninitialized: true }))

D. app.sessionMiddleware({ secret: 'keyboard cat' })

Solution

1. Step 1: Recall express-session syntax

   The middleware is added with app.use(session({ options })).

2. Step 2: Check options correctness

   Options like secret, resave, and saveUninitialized are standard.

3. Final Answer:

   app.use(session({ secret: 'keyboard cat', resave: false, saveUninitialized: true })) -> Option C

4. Quick Check:

   Use app.use(session({...})) with options [OK]

Hint: Use app.use(session({ secret, resave, saveUninitialized })) [OK]

Common Mistakes:

• Using app.session instead of app.use
• Passing secret as a string directly
• Calling non-existent methods like sessionMiddleware

3. Given this Express route using express-session:

app.get('/dashboard', (req, res) => {
  if (req.session.user) {
    res.send(`Welcome, ${req.session.user}!`);
  } else {
    res.status(401).send('Please log in');
  }
});

// Assume req.session.user = 'Alice'

What will the server respond when a logged-in user visits /dashboard?

medium

A. Welcome, Alice!

B. Please log in

C. Error: req.session.user is undefined

D. Redirect to login page

Solution

1. Step 1: Check session user existence

   The code checks if req.session.user exists; here it is 'Alice'.

2. Step 2: Determine response

   Since user exists, it sends Welcome, Alice! as response.

3. Final Answer:

   Welcome, Alice! -> Option A

4. Quick Check:

   Session user present = welcome message [OK]

Hint: If req.session.user exists, show welcome message [OK]

Common Mistakes:

• Assuming undefined session user causes error
• Expecting redirect without code
• Confusing status 401 with success message

4. Consider this code snippet for session setup:

const session = require('express-session');
app.use(session({
  secret: 'secret123',
  resave: false
}));

What is the likely problem with this setup?

medium

A. Session middleware must be added after routes

B. Missing saveUninitialized option may cause sessions not to save properly

C. resave must be true to save sessions

D. The secret should be a number, not a string

Solution

1. Step 1: Review required session options

   While secret and resave are set, saveUninitialized is missing.

2. Step 2: Understand saveUninitialized role

   Without saveUninitialized, some sessions may not be saved, causing unexpected behavior.

3. Final Answer:

   Missing saveUninitialized option may cause sessions not to save properly -> Option B

4. Quick Check:

   Always set saveUninitialized option [OK]

Hint: Always include saveUninitialized in session config [OK]

Common Mistakes:

• Thinking secret must be a number
• Believing resave must be true
• Adding middleware after routes

5. You want to protect a route so only logged-in users can access it using express-session. Which middleware function correctly checks the session and redirects unauthorized users to /login?

hard

A. function auth(req, res, next) { if (req.session.user) res.redirect('/login'); else next(); }

B. function auth(req, res) { if (!req.session.user) next(); else res.redirect('/login'); }

C. function auth(req, res, next) { if (req.session.user === undefined) res.send('Access granted'); else next(); }

D. function auth(req, res, next) { if (req.session.user) next(); else res.redirect('/login'); }

Solution

1. Step 1: Understand middleware signature

   Middleware must have (req, res, next) and call next() to continue.

2. Step 2: Check session user and redirect logic

   If req.session.user exists, call next() to allow access; otherwise redirect to /login.

3. Final Answer:

   function auth(req, res, next) { if (req.session.user) next(); else res.redirect('/login'); } -> Option D

4. Quick Check:

   Session user? next() : redirect [OK]

Hint: Call next() if logged in; else redirect to login [OK]

Common Mistakes:

• Missing next() call in middleware
• Reversing condition logic
• Sending response instead of redirecting