User login flow in Express - Mini Project: Build & Apply

User login flow

📖 Scenario: You are building a simple user login flow for a website using Express.js. Users will send their username and password to the server, and the server will check if the credentials are correct.

🎯 Goal: Create an Express.js server that accepts login requests, checks user credentials from a predefined list, and responds with success or failure messages.

📋 What You'll Learn

Create a users object with exact username-password pairs

Add a variable to hold the login success message

Write a POST route handler for '/login' that checks credentials

Send the correct response message based on login success or failure

💡 Why This Matters

🌍 Real World

User login flows are essential for websites and apps to authenticate users securely.

💼 Career

Understanding how to build login routes with Express is a key skill for backend web developers.

1

DATA SETUP: Create users data

Create a constant object called users with these exact entries: 'alice': 'wonderland', 'bob': 'builder', 'charlie': 'chocolate'.

Express

// Your code here

Need a hint?

Use a JavaScript object with usernames as keys and passwords as values.

2

CONFIGURATION: Add success message variable

Add a constant string variable called successMessage and set it to 'Login successful!'.

Express

const users = {
  'alice': 'wonderland',
  'bob': 'builder',
  'charlie': 'chocolate'
};

// Your code here

Need a hint?

Use const to create a string variable for the success message.

3

CORE LOGIC: Create login POST route

Write an Express POST route handler for '/login' that extracts username and password from req.body, checks if users[username] equals password, and stores the result in a boolean variable called isValidUser.

Express

const users = {
  'alice': 'wonderland',
  'bob': 'builder',
  'charlie': 'chocolate'
};

const successMessage = 'Login successful!';

const express = require('express');
const app = express();
app.use(express.json());

// Your code here

Need a hint?

Use app.post with a callback that destructures username and password from req.body.

4

COMPLETION: Send response based on login result

Inside the /login route handler, send a JSON response with { message: successMessage } if isValidUser is true, otherwise send { message: 'Invalid username or password' }. Then, start the Express server listening on port 3000.

Express

const users = {
  'alice': 'wonderland',
  'bob': 'builder',
  'charlie': 'chocolate'
};

const successMessage = 'Login successful!';

const express = require('express');
const app = express();
app.use(express.json());

app.post('/login', (req, res) => {
  const { username, password } = req.body;
  const isValidUser = users[username] === password;
  // Your code here
});

// Your code here

Need a hint?

Use res.json() to send the response and app.listen(3000) to start the server.