Implementing OAuth2 PKCE with Spring Boot and Spring Security

Hello, Spring enthusiasts! 👋 Today, we’re going to explore how to implement Proof Key for Code Exchange (PKCE) using Spring Boot and Spring Security. PKCE is an extension to the OAuth2 Authorization Code Flow that enhances security, especially for public clients like mobile and single-page applications.

Understanding OAuth2 PKCE

PKCE (pronounced "pixy") is designed to protect the authorization code flow in OAuth2 from certain attacks, such as authorization code interception. It involves the client generating a code verifier and a code challenge. The code challenge is sent to the authorization server during the authorization request, and the code verifier is sent during the token request. The server then verifies that the code verifier matches the code challenge.

Steps to Implement PKCE

Set Up the Spring Boot Project: Start by creating a new Spring Boot project with the necessary dependencies.
Configure Security: Set up Spring Security to handle OAuth2 authentication and authorization.
Create the Authorization Endpoint: Implement the endpoint to handle authorization requests with PKCE.
Create the Token Endpoint: Implement the endpoint to handle token requests with PKCE.
Handle PKCE Logic: Write the logic to generate and validate the code verifier and code challenge.
Test the Flow: Ensure the flow works correctly by testing it with various clients.

Step 1: Set Up the Spring Boot Project

First, create a new Spring Boot project using Spring Initializr or your favorite IDE. Add the following dependencies:

Spring Web
Spring Security
Spring Security OAuth2 Resource Server
Spring Security OAuth2 Authorization Server

Step 2: Configure Security

In your application.yml or application.properties, configure the security settings:


spring:
  security:
    oauth2:
      authorizationserver:
        issuer-uri: https://your-issuer-uri

Step 3: Create the Authorization Endpoint

Create a new controller to handle the authorization requests with PKCE:


import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class AuthorizationController {

    @GetMapping("/oauth2/authorize")
    public AuthorizationResponse authorize(@RequestParam String responseType,
                                           @RequestParam String clientId,
                                           @RequestParam String redirectUri,
                                           @RequestParam String codeChallenge,
                                           @RequestParam String codeChallengeMethod) {
        // Implement authorization logic with PKCE here
        return new AuthorizationResponse(authorizationCode);
    }
}

Step 4: Create the Token Endpoint

Create a new controller to handle the token requests with PKCE:


import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class TokenController {

    @PostMapping("/oauth2/token")
    public TokenResponse exchangeCode(@RequestBody TokenRequest request) {
        // Implement token exchange logic with PKCE here
        return new TokenResponse(accessToken, refreshToken, expiresIn);
    }
}

Step 5: Handle PKCE Logic

Implement the logic to generate and validate the code verifier and code challenge:


import org.springframework.stereotype.Service;
import java.util.Base64;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

@Service
public class PkceService {

    public String generateCodeChallenge(String codeVerifier) throws NoSuchAlgorithmException {
        byte[] bytes = codeVerifier.getBytes();
        MessageDigest md = MessageDigest.getInstance("SHA-256");
        byte[] digest = md.digest(bytes);
        return Base64.getUrlEncoder().withoutPadding().encodeToString(digest);
    }

    public boolean validateCodeVerifier(String codeVerifier, String codeChallenge) throws NoSuchAlgorithmException {
        String generatedCodeChallenge = generateCodeChallenge(codeVerifier);
        return generatedCodeChallenge.equals(codeChallenge);
    }
}

Step 6: Test the Flow

Use tools like Postman or curl to test the flow. Ensure that the PKCE authorization and token exchange processes work correctly and handle various scenarios, such as valid and invalid code verifiers, expired codes, and successful token exchanges.

Conclusion

Implementing OAuth2 PKCE in Spring Boot with Spring Security enhances your application's security by protecting the authorization code flow from interception attacks. By following these steps, you can efficiently manage PKCE and ensure secure communication between clients and your server. Happy coding! 🚀

Hope this helps you in your Spring journey! Keep exploring and coding. 😊

OAuth2 PKCE with Spring Boot