1. Introduction

In this tutorial, we'll delve into the basics of password-based authentication. Our main goal is to understand how to implement a simple form of security that requires a username and password to gain access.

By the end of this tutorial, you will learn:
- How password-based authentication works
- How to implement password-based authentication in your web applications

Prerequisites: Basic understanding of HTML, CSS, JavaScript, and Node.js.

2. Step-by-Step Guide

What is Password-Based Authentication?

This is a security mechanism used to authenticate and authorize a user by requiring them to present a password. When a user first registers, their password is stored securely. Each time they log in, the password provided is compared with the one stored. If they match, the user is granted access.

Implementing Password-Based Authentication

For our example, we'll be using Node.js and a package called bcryptjs for hashing passwords.

1. Install bcryptjs
You can install this package through npm.

npm install bcryptjs

2. Hashing User Password
When a user registers, instead of storing their password in plaintext, we'll hash it.

const bcrypt = require('bcryptjs');

let password = "userpassword";
let hashedPassword = bcrypt.hashSync(password, 8);

3. Comparing User Password
When a user logs in, we compare the password they provided with the hashed password stored.

let loginPassword = "userpassword";
let isMatch = bcrypt.compareSync(loginPassword, hashedPassword);

3. Code Examples

Example 1: User Registration

// Importing required modules
const express = require('express');
const bcrypt = require('bcryptjs');

// Setting up express
let app = express();
app.use(express.json());

// In-memory store for users
let users = {};

// User registration
app.post('/register', (req, res) => {
    // Hashing user password
    let hashedPassword = bcrypt.hashSync(req.body.password, 8);

    // Storing user details
    users[req.body.username] = hashedPassword;
    res.send('User registered successfully!');
});

// Starting server
app.listen(3000, () => console.log('Server started on port 3000!'));

Example 2: User Login

// User login
app.post('/login', (req, res) => {
    // Checking if user exists
    if(!users[req.body.username]) {
        return res.status(400).send('User not found!');
    }

    // Comparing passwords
    let isMatch = bcrypt.compareSync(req.body.password, users[req.body.username]);

    if(isMatch) {
        res.send('Logged in successfully!');
    } else {
        res.status(400).send('Password is incorrect!');
    }
});

4. Summary

In this tutorial, we covered the basics of password-based authentication. We learned how to hash a password during user registration and how to compare a hashed password during user login using bcryptjs.

To further your learning, you can explore how to use secure cookies or tokens (like JWT) to manage user sessions. You can also learn about salting hashes for additional security.

5. Practice Exercises

1. Extend the login script to include a registration limit.
- After 3 failed attempts, the user should be blocked for a certain period of time.

2. Implement an option for users to reset their password.
- The user should be able to enter their email address and receive a password reset link.

3. Implement two-factor authentication.
- After successfully entering their password, the user should receive a code via email that they need to enter to log in.

These exercises will help you improve your understanding of password-based authentication. Try to implement them using the knowledge you've gained from this tutorial.