Implementing Spring Boot and JWT: A Step-by-Step Guide

As a Java developer, you’re likely familiar with the importance of authentication and authorization in web applications. JSON Web Tokens (JWT) have become a popular choice for implementing authentication in modern web apps. In this blog post, we’ll explore how to implement Spring Boot and JWT together to secure your web application.

What is JWT?

JSON Web Token (JWT) is a compact, URL-safe means of representing claims to be transferred between two parties. The token is digitally signed and contains the user’s information, such as their username, email, or role. JWTs are typically used for authentication purposes but can also be used for authorization.

Spring Boot and JWT: A Perfect Pair

Spring Boot provides a simple way to implement web applications using Java. When combined with JWT, Spring Boot makes it easy to secure your application by implementing authentication and authorization mechanisms.

Here’s how you can implement Spring Boot and JWT together:

Step 1: Add Dependencies

First, add the following dependencies to your pom.xml file

<dependency>
    <groupId>io.jsonwebtoken</groupId>
    <artifactId>jjwt-api</artifactId>
    <version>0.9.1</version>
</dependency>

<dependency>
    <groupId>io.jsonwebtoken</groupId>
    <artifactId>jjwt-impl</artifactId>
    <version>0.9.1</version>
</dependency>

<dependency>
    <groupId>io.jsonwebtoken</groupId>
    <artifactId>jjwt-generator</artifactId>
    <version>0.9.1</version>
</dependency>

Step 2: Configure JWT

Create a config package and create a JwtConfig class to configure JWT:

package com.example.config;

import io.jsonwebtoken.Claims;
import io.jsonwebtoken.Jws;
import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

import java.util.Date;
import java.util.BaseSpringSource;

@Slf4j
@Component
public class JwtConfig {

    @Value("${jwt.secret}")
    private String jwtSecret;

    public String generateToken(String username) {
        return Jwts.builder()
                .setSubject(username)
                .signWith(SignatureAlgorithm.HS256, jwtSecret)
                .compact();
    }

    public Jws<Claims> verifyToken(String token) {
        return Jwts.parser().setSubject(token).parseClaimsJws(token);
    }
}

Step 3: Implement Authentication

Create a UserDetailsService class to implement user authentication:

package com.example.service;

import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.security.core.userdetails.UserDetailsService;
import org.springframework.security.core.userdetails.UsernameNotFoundException;

public interface UserDetailsService extends UserDetailsService {

    @Override
    UserDetails loadUserByUsername(String username) throws UsernameNotFoundException;

    default public UserDetails loadUserByUsername(String username, String password) throws UsernameNotFoundException {
        // implement user authentication logic here
    }
}

Step 4: Implement Authorization

Create an AccessDecisionManager class to implement access decision management:

package com.example.manager;

import org.springframework.security.access.AccessDecisionManager;
import org.springframework.security.core.Authentication;
import org.springframework.security.core.context.SecurityContextHolder;

public interface AccessDecisionManager extends AccessDecisionManager {

    @Override
    boolean decide(Authentication authentication, Object object) throws AccessDeniedException;

    default public boolean decide(Authentication authentication, Object object, String role) {
        // implement access decision logic here
    }
}

Step 5: Implement Spring Security

Configure Spring Security to use the JWT-based authentication and authorization mechanism:

package com.example.config;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.security.authentication.AuthenticationManager;
import org.springframework.security.authentication.dao.DaoAuthenticationProvider;
import org.springframework.security.core.Authentication;
import org.springframework.security.core.context.SecurityContextHolder;

public class SecurityConfig implements WebSecurityConfigurerAdapter {

    @Autowired
    private AuthenticationManager authenticationManager;

    @Override
    public void configure(WebSecurity web) {
        web.ignoring()
                .antMatchers("/login")
                .anyRequest();
    }

    @Bean
    public DaoAuthenticationProvider daoAuthenticationProvider() {
        return new DaoAuthenticationProvider(authenticationManager);
    }
}

That’s it! You’ve successfully implemented Spring Boot and JWT together to secure your web application.

Conclusion

In this blog post, we explored how to implement Spring Boot and JWT together to secure a web application. By following these steps, you can create a robust authentication and authorization mechanism using JWT-based tokens. Remember to always keep security in mind when building applications that handle sensitive data.