Custom Access Token - Spring Authorization Server

Spring Authorization Server (SAS) is a Spring Framework project that provides the functionality to create and manage OAuth 2.0 and OpenID Connect (OIDC) based authorization servers. SAS is built on top of Spring Security, and it provides a comprehensive set of features that can be used to secure your APIs and web applications.

SAS generates access tokens using JSON Web Tokens (JWT). A JWT is a compact, URL-safe means of representing claims to be transferred between two parties. JWTs are signed using a secret or public/private key pair, which ensures that the token has not been tampered with.

When a client requests an access token, SAS generates a JWT that contains the requested claims (scopes), the client ID, and the token expiration time. The JWT is signed using the server's private key, and the resulting access token is returned to the client.

You can customize the access token generation process in SAS by implementing the OAuth2TokenCustomizer interface. This interface provides a method called customize(), which is called before the access token is generated. In the customize() method, you can modify the token request and response objects to customize the access token generation process.

Here is an example of how to customize the access token generation process in SAS:

@Configuration
public class AuthorizationServerConfig {

    @Autowired
    private OAuth2TokenCustomizer<JwtEncodingContext> customizer;

    @Bean
    public RegisteredClientRepository registeredClientRepository() {
        RegisteredClient registeredClient = RegisteredClient.withId(UUID.randomUUID().toString())
                .clientId("client")
                .clientSecret("secret")
                .clientAuthenticationMethod(ClientAuthenticationMethod.CLIENT_SECRET_BASIC)
                .authorizationGrantType(AuthorizationGrantType.AUTHORIZATION_CODE)
                .redirectUri("http://localhost:8080/login/oauth2/code/custom")
                .scope("openid", "profile", "email")
                .clientSettings(ClientSettings.builder().requireAuthorizationConsent(true).build())
                .build();
        return new InMemoryRegisteredClientRepository(registeredClient);
    }

    @Bean
    public OAuth2AuthorizationServer authorizationServer() {
        OAuth2AuthorizationServerBuilder builder = OAuth2AuthorizationServer.withRegisteredClientRepository(this::registeredClientRepository);
        builder.tokenCustomizer(customizer);
        // ...
        return builder.build();
    }
}

In this example, we are injecting an OAuth2TokenCustomizer object into our configuration class using Spring's @Autowired annotation. We then pass this customizer object to the OAuth2AuthorizationServerBuilder using the tokenCustomizer() method.

You can implement the OAuth2TokenCustomizer interface to customize the access token generation process according to your needs. For example, you can modify the token claims, add custom headers, or perform additional checks before the token is generated. Here is an example of how to modify the access token claims:

@Component
public class CustomTokenCustomizer implements OAuth2TokenCustomizer<JwtEncodingContext> {

    @Override
    public void customize(JwtEncodingContext context) {
        OAuth2AccessToken token = context.getAccessToken();
        Jwt.Builder builder = Jwt.withTokenValue(token.getTokenValue());
        builder.header("alg", "HS256");
        builder.claim("custom_claim", "custom_value");
        context.setJwt(builder.build());
    }
}

In this example, we are adding a custom claim called custom_claim with the value custom_value to the access token. We are also setting the alg header to HS256 to specify the JWT signature algorithm.

I hope this helps you understand how SAS generates access tokens and how to customize the access token generation process.