Implementing Authentication in Next.js

What You’ll Learn 📚

• Core concepts of authentication
• Key terminology
• Simple to complex examples
• Common questions and answers
• Troubleshooting tips

Introduction to Authentication

Authentication is the process of verifying who a user is. It’s like checking your ID at a club—only those who prove their identity get access. In web applications, authentication ensures that users are who they claim to be, allowing them to access protected resources.

Core Concepts

• Authentication: Verifying the identity of a user.
• Authorization: Determining what resources a user can access.
• Session: A way to store user data between requests.
• JWT (JSON Web Token): A compact, URL-safe means of representing claims to be transferred between two parties.

Key Terminology

Authentication is about identity verification, while authorization is about permission.

Getting Started: The Simplest Example

Let’s start with a basic example using Next.js and a simple form to simulate authentication.

import { useState } from 'react';

export default function Login() {
  const [username, setUsername] = useState('');
  const [password, setPassword] = useState('');

  const handleSubmit = (e) => {
    e.preventDefault();
    // Simulate a login
    if (username === 'student' && password === 'password') {
      alert('Login successful! 🎉');
    } else {
      alert('Invalid credentials, please try again.');
    }
  };

  return (
    

       setUsername(e.target.value)}
      />
       setPassword(e.target.value)}
      />
      Login
    
  );
}

Expected Output

Progressively Complex Examples

Example 1: Using Sessions

Let’s enhance our example by using sessions to maintain user state.

// Install the necessary package
// npm install next-session

import { useState } from 'react';
import { useSession, signIn, signOut } from 'next-auth/client';

export default function Auth() {
  const [session, loading] = useSession();

  return (
    

      {!session && (
         signIn()}>Sign in
      )}
      {session && (
        <>
          
Welcome, {session.user.name}!
           signOut()}>Sign out
        
      )}
    
  );
}

Expected Output

Example 2: JWT Authentication

Now, let’s implement JWT authentication for a more secure approach.

// Install jsonwebtoken
// npm install jsonwebtoken

import jwt from 'jsonwebtoken';

export default function handler(req, res) {
  const { username, password } = req.body;

  if (username === 'student' && password === 'password') {
    const token = jwt.sign({ username }, 'secret', { expiresIn: '1h' });
    res.status(200).json({ token });
  } else {
    res.status(401).json({ error: 'Invalid credentials' });
  }
}

Expected Output

Example 3: Protecting Routes

Finally, let’s protect a route using the JWT token.

import jwt from 'jsonwebtoken';

export default function handler(req, res) {
  const token = req.headers.authorization;

  if (!token) {
    return res.status(401).json({ error: 'No token provided' });
  }

  jwt.verify(token, 'secret', (err, decoded) => {
    if (err) {
      return res.status(401).json({ error: 'Invalid token' });
    }
    res.status(200).json({ message: 'Protected content', user: decoded.username });
  });
}

Expected Output

Common Questions and Answers

1. What is the difference between authentication and authorization?

   Authentication verifies who you are, while authorization determines what you can do.

2. Why use JWT for authentication?

   JWTs are compact, self-contained, and can be easily used across different domains.

3. How do I store JWTs securely?

   Store JWTs in secure, HTTP-only cookies to prevent XSS attacks.

4. What is a session?

   A session is a way to persist user data across requests, typically stored on the server.

5. How do I protect routes in Next.js?

   Use middleware or server-side logic to check authentication before serving protected routes.

Troubleshooting Common Issues

Issue: Invalid Credentials

Ensure your username and password match the expected values in your authentication logic.

Issue: JWT Expired

Check the token’s expiration time and ensure it’s refreshed or reissued before it expires.

Issue: No Token Provided

Make sure to include the token in the request headers when accessing protected routes.

Practice Exercises

• Create a registration form and store user credentials securely.
• Implement a password reset feature.
• Use a third-party authentication provider like Google or GitHub.

Additional Resources

• NextAuth.js Documentation
• JWT.io
• Next.js Documentation

Congratulations on completing this tutorial! 🎉 You’ve learned how to implement authentication in Next.js, from basic forms to JWT and protected routes. Keep practicing, and soon you’ll be a pro at securing your web applications. Happy coding! 💻