Building a Secure Authentication System with Spring Boot and JWT

Authentication is the cornerstone of modern web applications. In this guide, I'll walk you through building a production-ready authentication system using Spring Boot and JWT tokens.

Why JWT?

JSON Web Tokens (JWT) provide a stateless authentication mechanism that's perfect for modern microservices architectures. Unlike session-based authentication, JWTs don't require server-side storage, making them highly scalable.

Architecture Overview

Our authentication system will have three main components:

1. Authentication Filter - Intercepts requests and validates tokens
2. Token Service - Generates and validates JWT tokens
3. User Service - Manages user credentials and roles

Implementation

1. Setting Up Dependencies

First, add the required dependencies to your pom.xml:

<dependency>
    <groupId>io.jsonwebtoken</groupId>
    <artifactId>jjwt-api</artifactId>
    <version>0.11.5</version>
</dependency>

2. Creating the Token Service

The token service handles JWT generation and validation:

@Service
class TokenService {
    private val secretKey = Keys.secretKeyFor(SignatureAlgorithm.HS256)
    
    fun generateToken(username: String): String {
        return Jwts.builder()
            .setSubject(username)
            .setIssuedAt(Date())
            .setExpiration(Date(System.currentTimeMillis() + 86400000))
            .signWith(secretKey)
            .compact()
    }
}

3. Implementing Refresh Tokens

Refresh tokens extend session lifetime securely. Store them in Redis with TTL:

@Service
class RefreshTokenService(
    private val redisTemplate: RedisTemplate<String, String>
) {
    fun createRefreshToken(username: String): String {
        val token = UUID.randomUUID().toString()
        redisTemplate.opsForValue()
            .set("refresh:$username", token, 7, TimeUnit.DAYS)
        return token
    }
}

Security Best Practices

1. Use strong secret keys - Never hardcode secrets
2. Implement token rotation - Refresh tokens should be single-use
3. Set appropriate expiration - Access tokens: 15 min, Refresh: 7 days
4. Validate on every request - Don't trust client-side validation

Testing Your Implementation

Always test your authentication flow:

@Test
fun `should generate valid JWT token`() {
    val token = tokenService.generateToken("testuser")
    val claims = tokenService.validateToken(token)
    assertEquals("testuser", claims.subject)
}

Conclusion

Building a secure authentication system requires careful consideration of security best practices. The implementation shown here provides a solid foundation that you can extend based on your specific requirements.

Next Steps:

• Add OAuth2 support for social login
• Implement rate limiting
• Add two-factor authentication
• Monitor token usage patterns

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Have questions about this implementation? Feel free to reach out!