How do you implement JWT authentication in Spring Boot?

Table of Contents

• Introduction
• Steps to Implement JWT Authentication in Spring Boot
  • 1. Add Required Dependencies
    • Maven:
    • Gradle:
  • 2. Create JWT Utility Class
  • Explanation:
  • 3. Create a Filter for JWT Authentication
  • Explanation:
  • 4. Configure Spring Security
  • Explanation:
  • 5. Create Authentication Controller
  • Explanation:
• Conclusion

Introduction

JWT (JSON Web Token) is a compact, URL-safe token that is commonly used for authentication and authorization in web applications. JWT allows for stateless authentication, meaning that user sessions do not need to be stored on the server side. Instead, the server can verify the authenticity of requests using the JWT, which contains claims about the user.

In a Spring Boot application, JWT authentication is a popular way to secure REST APIs. By using JWT, you can manage authentication without storing sessions or relying on cookies, which is especially useful in modern applications such as microservices or stateless RESTful APIs.

This guide will walk you through the steps of implementing JWT-based authentication in a Spring Boot application.

Steps to Implement JWT Authentication in Spring Boot

1. Add Required Dependencies

First, you need to add the required dependencies in your pom.xml (for Maven) or build.gradle (for Gradle). These dependencies include Spring Boot Security, Spring Web, and JWT libraries.

Maven:

Gradle:

2. Create JWT Utility Class

Next, you need to create a utility class that will handle the JWT generation and validation. The class will have methods to:

• Generate a JWT token using user credentials (such as username).
• Validate the JWT token and extract user information.

Here's an example of a JwtUtil class:

Explanation:

• **generateToken(String username)**: Generates a JWT token with the given username and a predefined expiration time.
• **extractUsername(String token)**: Extracts the username (subject) from the token.
• **validateToken(String token, String username)**: Validates if the token is expired and matches the username.

3. Create a Filter for JWT Authentication

You need to create a filter that intercepts incoming requests and checks whether the request contains a valid JWT token. If a valid token is found, the filter will authenticate the user.

Here's an example of a JwtAuthenticationFilter class:

Explanation:

• **doFilterInternal()**: The filter extracts the token from the Authorization header, validates it, and sets the authentication context if the token is valid.

4. Configure Spring Security

You need to configure Spring Security to use your custom JWT filter. This involves creating a SecurityConfig class to configure HTTP security and add the filter.

Here's an example of a basic security configuration:

Explanation:

• **addFilter(new JwtAuthenticationFilter(jwtUtil))**: Adds the JwtAuthenticationFilter to the security filter chain.
• **antMatchers("/login", "/register").permitAll()**: Allows unauthenticated access to specific endpoints such as /login and /register.

5. Create Authentication Controller

You need an endpoint to authenticate users and issue a JWT token after successful login. Here's an example of a AuthController:

Explanation:

• **/login** endpoint: The login() method checks the username and password, and returns a JWT token if authentication is successful.

Conclusion

Implementing JWT authentication in Spring Boot allows you to build a secure, stateless authentication system for your application. By generating a JWT token upon user login and verifying it with each request, you can effectively authenticate users without needing to manage server-side sessions. This approach is particularly useful for securing REST APIs or building microservices.

In this guide, we covered the key steps, including adding dependencies, creating JWT utility and filter classes, configuring Spring Security, and setting up authentication endpoints. With these steps, you'll be able to implement JWT authentication in your Spring Boot application efficiently.