Testing authentication flows in Express - Mini Project: Build & Apply

Testing authentication flows

📖 Scenario: You are building a simple Express server that handles user login authentication. You want to test the authentication flow to ensure users can log in with correct credentials and are rejected otherwise.

🎯 Goal: Build a basic Express app with a user data setup, a configuration for a test user, a login route that checks credentials, and a final middleware to handle authentication results.

📋 What You'll Learn

Create a user data object with a username and password

Add a configuration variable for the test username

Implement a login route that checks the username and password

Add a middleware that sends a success or failure response

💡 Why This Matters

🌍 Real World

Testing authentication flows is essential for any web app that requires user login. This ensures only valid users can access protected resources.

💼 Career

Understanding how to build and test authentication routes is a key skill for backend developers working with Express or similar frameworks.

1

DATA SETUP: Create user data

Create a constant object called users with one entry: username 'testuser' and password 'mypassword'.

Express

// Your code here

Need a hint?

Use a JavaScript object to store username and password pairs.

2

CONFIGURATION: Add test username

Add a constant called testUsername and set it to the string 'testuser'.

Express

const users = { 'testuser': 'mypassword' };
// Your code here

Need a hint?

This variable will help us check the login for this specific user.

3

CORE LOGIC: Implement login route

Create an Express POST route at /login that reads username and password from req.body. Check if users[username] equals password. If yes, set req.authenticated = true, else req.authenticated = false.

Express

const users = { 'testuser': 'mypassword' };
const testUsername = 'testuser';

import express from 'express';
const app = express();
app.use(express.json());

// Your code here

Need a hint?

Use req.body to get login data and set a flag req.authenticated accordingly.

4

COMPLETION: Add response middleware

Add a middleware after the login route that sends a JSON response with { success: true } if req.authenticated is true, else { success: false }. Export the app object.

Express

const users = { 'testuser': 'mypassword' };
const testUsername = 'testuser';

import express from 'express';
const app = express();
app.use(express.json());

app.post('/login', (req, res, next) => {
    const { username, password } = req.body;
    if (users[username] === password) {
        req.authenticated = true;
    } else {
        req.authenticated = false;
    }
    next();
});

// Your code here

Need a hint?

This middleware sends the final response based on authentication result.