Spring Authorization Server - Quick Reference

Full Reference: See advanced.md for JPA client persistence, JWT configuration, custom token claims, user info endpoint, consent controller, token revocation, resource server integration, and testing.

Deep Knowledge: Use mcp__documentation__fetch_docs with technology: spring-authorization-server for comprehensive documentation.

Dependencies

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-oauth2-authorization-server</artifactId>
</dependency>

OAuth 2.1 Flows

Authorization Code + PKCE:

Client ──(1) Authorization Request + code_challenge──▶ Auth Server
      ◀──(2) Authorization Code──────────────────────
      ──(3) Token Request + code_verifier────────────▶
      ◀──(4) Access Token + Refresh Token + ID Token─

Basic Configuration

@Configuration
@EnableWebSecurity
public class SecurityConfig {

    @Bean
    @Order(1)
    public SecurityFilterChain authorizationServerSecurityFilterChain(HttpSecurity http)
            throws Exception {
        OAuth2AuthorizationServerConfiguration.applyDefaultSecurity(http);

        http.getConfigurer(OAuth2AuthorizationServerConfigurer.class)
            .oidc(Customizer.withDefaults());  // Enable OpenID Connect

        http.exceptionHandling(exceptions -> exceptions
                .defaultAuthenticationEntryPointFor(
                    new LoginUrlAuthenticationEntryPoint("/login"),
                    new MediaTypeRequestMatcher(MediaType.TEXT_HTML)
                )
            )
            .oauth2ResourceServer(oauth2 -> oauth2.jwt(Customizer.withDefaults()));

        return http.build();
    }

    @Bean
    @Order(2)
    public SecurityFilterChain defaultSecurityFilterChain(HttpSecurity http) throws Exception {
        http.authorizeHttpRequests(authorize -> authorize.anyRequest().authenticated())
            .formLogin(Customizer.withDefaults());
        return http.build();
    }
}

Client Registration

@Bean
public RegisteredClientRepository registeredClientRepository() {
    RegisteredClient webClient = RegisteredClient.withId(UUID.randomUUID().toString())
        .clientId("web-client")
        .clientSecret("{noop}secret")
        .clientAuthenticationMethod(ClientAuthenticationMethod.CLIENT_SECRET_BASIC)
        .authorizationGrantType(AuthorizationGrantType.AUTHORIZATION_CODE)
        .authorizationGrantType(AuthorizationGrantType.REFRESH_TOKEN)
        .redirectUri("http://localhost:8080/login/oauth2/code/web-client")
        .scope(OidcScopes.OPENID)
        .scope(OidcScopes.PROFILE)
        .scope("read")
        .clientSettings(ClientSettings.builder()
            .requireAuthorizationConsent(true)
            .requireProofKey(true)  // PKCE required
            .build())
        .tokenSettings(TokenSettings.builder()
            .accessTokenTimeToLive(Duration.ofMinutes(15))
            .refreshTokenTimeToLive(Duration.ofDays(7))
            .reuseRefreshTokens(false)
            .build())
        .build();

    return new InMemoryRegisteredClientRepository(webClient);
}

Best Practices

Do	Don't
Require PKCE for public clients	Allow plain authorization code
Use short-lived access tokens	Long-lived access tokens
Rotate refresh tokens	Reuse refresh tokens indefinitely
Store keys securely (Vault)	Hardcode keys in config
Validate redirect URIs strictly	Allow open redirects

When NOT to Use This Skill

• OAuth2 Client Configuration - Use spring-security
• Resource Server - For validating JWT tokens use spring-security
• Basic Authentication - Use spring-security
• Session Management - Use spring-session

Anti-Patterns

Anti-Pattern	Why It's Bad	Better Approach
Reusing refresh tokens	Security risk if compromised	Rotate on each use
Long-lived access tokens	Increased exposure window	Keep to 15-30 min
Hardcoded client secrets	Secrets in version control	Use secret management
No PKCE for SPAs	Code interception vulnerability	Always require PKCE
Wildcard redirect URIs	Open redirect vulnerability	Whitelist exact URIs

Quick Troubleshooting

Issue	Possible Cause	Solution
401 at /oauth2/authorize	User not authenticated	Check SecurityFilterChain order
Invalid client error	Client not registered	Verify RegisteredClientRepository
JWKS endpoint 404	JWKSource bean missing	Ensure JWKSource configured
Token validation fails	Issuer mismatch	Check issuer URL matches
PKCE validation fails	code_verifier mismatch	Verify PKCE implementation

Production Checklist

• HTTPS everywhere
• RSA keys in secure storage
• Client secrets encrypted
• PKCE required for public clients
• Token lifetimes configured
• Consent flow implemented
• Token revocation working
• Rate limiting enabled
• Audit logging configured

Reference Documentation

• Spring Authorization Server Reference
• OAuth 2.1 Specification