Session-based auth with express-session - Mini Project: Build & Apply

Session-based auth with express-session

📖 Scenario: You are building a simple web server that lets users log in and keeps them logged in using sessions. This means the server remembers who the user is between page visits.We will use the express-session library to handle sessions in Express.

🎯 Goal: Create an Express server that uses express-session to store user login state. You will set up session middleware, create a login route that saves the username in the session, and a protected route that only logged-in users can access.

📋 What You'll Learn

Create an Express app with express-session middleware

Set a session secret in the configuration

Create a /login POST route that saves req.body.username in req.session.username

Create a /dashboard GET route that checks if req.session.username exists and responds accordingly

💡 Why This Matters

🌍 Real World

Session-based authentication is common in websites to remember logged-in users without asking for credentials every time.

💼 Career

Understanding session management is essential for backend developers working with user authentication and stateful web applications.

1

Setup Express app and import express-session

Create an Express app by requiring express and express-session. Then call express() and store it in a variable called app.

Express

const express = require('express');
const session = require('express-session');
const app = express();
// Your code here

Hint

Use require('express') and require('express-session') to import the modules. Then create the app with express().

2

Configure express-session middleware

Add the express-session middleware to app using app.use(). Use a session secret string 'mysecret' in the configuration object.

Express

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

app.use(session({ secret: 'mysecret', resave: false, saveUninitialized: true }));
// Your code here

Hint

Use app.use(session({ secret: 'mysecret', resave: false, saveUninitialized: true })) to add session support.

3

Create /login POST route to save username in session

Add a POST route /login to app. Inside the route handler, save req.body.username to req.session.username. Use express.json() middleware to parse JSON bodies.

Express

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

app.use(session({ secret: 'mysecret', resave: false, saveUninitialized: true }));
app.use(express.json());

app.post('/login', (req, res) => {
    // Your code here
});

Hint

Use app.post('/login', (req, res) => { ... }). Inside, assign req.session.username = req.body.username and send a response.

4

Create /dashboard GET route to check session and respond

Add a GET route /dashboard to app. Inside the handler, check if req.session.username exists. If yes, respond with Welcome, {username}. Otherwise, respond with Access denied.

Express

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

app.use(session({ secret: 'mysecret', resave: false, saveUninitialized: true }));
app.use(express.json());

app.post('/login', (req, res) => {
    req.session.username = req.body.username;
    res.send('Logged in');
});

app.get('/dashboard', (req, res) => {
    // Your code here
});

Hint

Use app.get('/dashboard', (req, res) => { ... }). Check req.session.username and respond accordingly.

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