Introduction

In this tutorial, you will learn to build a custom authentication and login system from scratch. Authentication is a critical element of web development as it controls user access to your application and ensures data security. By building a custom authentication system, you will gain a better understanding of the underlying processes and have greater control over your application's security.

By the end of this tutorial, you will learn:
- How to set up a user database
- How to create a registration form
- How to handle login and logout functionality
- How to keep sessions secure

Prerequisites: Basic knowledge of HTML, CSS, JavaScript, and a server-side language like PHP or Node.js. Familiarity with databases (like MySQL) and web servers (like Apache) is also beneficial.

Step-by-Step Guide

1. Setting Up the User Database
   You'll first need to set up a database to store user data. Each user should have a unique username or email and a securely hashed password. It's best practice to never store passwords in plaintext.

2. Creating a Registration Form
   You'll need a form where new users can register. This form should collect a username/email and password at minimum. It's best practice to validate this information before storing it in your database.

3. Handling Login and Logout
   After registration, users should be able to log in and out. In this step, you'll create a login form and a session that persists until the user logs out.

4. Session Security
   It's critical to secure user sessions to prevent unauthorized access. You'll learn to implement techniques like session timeouts and regeneration.

Code Examples

1. User Registration

// Registration form submit event handler
form.onsubmit = async (e) => {
  e.preventDefault();

  // Collect form data
  let formData = new FormData(form);
  let email = formData.get('email');
  let password = formData.get('password');

  // Hash password
  let hashedPassword = await bcrypt.hash(password, 10);

  // Save user to database
  db.collection('users').insertOne({email, password: hashedPassword});
};

This code captures user data from a form, hashes the password using bcrypt, and stores the user data in a MongoDB database.

1. User Login

// Login form submit event handler
form.onsubmit = async (e) => {
  e.preventDefault();

  // Collect form data
  let formData = new FormData(form);
  let email = formData.get('email');
  let password = formData.get('password');

  // Retrieve user from database
  let user = await db.collection('users').findOne({email});

  // Verify password
  if (await bcrypt.compare(password, user.password)) {
    // Start session
    session.start(user);
  } else {
    alert('Invalid login credentials');
  }
};

This code handles a login form submission. It retrieves the user from the database, verifies the password, and starts a session if the password is correct.

Summary

In this tutorial, we've covered the basics of setting up a custom authentication and login system, including user registration, login, and session security. Building these systems from scratch can be complex, but it provides valuable insight into their inner workings.

Practice Exercises

1. Exercise 1
   Implement a feature that requires users to confirm their password during registration.

2. Exercise 2
   Add a "Remember Me" checkbox to the login form that keeps the user logged in even after closing the browser.

3. Exercise 3
   Implement password reset functionality that allows users to reset their password via email.

Solutions

1. Solution 1
   Add another password field to the registration form and check that both passwords match before hashing and storing the password.

2. Solution 2
   Use cookies to store the session ID on the client side. If the "Remember Me" checkbox is ticked, set the cookie to expire at a far future date; otherwise, set it to expire when the browser closes.

3. Solution 3
   Generate a unique reset token, send it to the user's email, and store it in the database. When the user clicks the link in the email, verify the token, allow them to enter a new password, and then hash and store the new password.

Keep practicing and experimenting with different features to improve your understanding of authentication systems. Happy coding!