Spring Boot + Spring Security OAuth2: Why Your Resource Server Isn't Talking to the Authorization Server at Startup
The Problem: Silent Startup
You've meticulously set up your Spring Boot application, equipped with Spring Security OAuth2 to secure your resources with JWTs. But, during startup, you notice a strange behavior: the resource server isn't contacting the authorization server to fetch its keys or metadata. It just sits there, seemingly oblivious to the need for validation.
The Scenario
Let's illustrate this scenario with a code snippet:
@Configuration
@EnableAuthorizationServer
public class AuthorizationServerConfig extends AuthorizationServerConfigurerAdapter {
@Override
public void configure(ClientDetailsServiceConfigurer clients) throws Exception {
clients.inMemory()
.withClient("my-client")
.secret("my-secret")
.authorizedGrantTypes("password", "refresh_token")
.scopes("read", "write")
.accessTokenValiditySeconds(3600)
.refreshTokenValiditySeconds(2592000);
}
// ... other configurations ...
}
@Configuration
@EnableResourceServer
public class ResourceServerConfig extends ResourceServerConfigurerAdapter {
@Override
public void configure(HttpSecurity http) throws Exception {
http
.authorizeRequests()
.antMatchers("/api/**").authenticated()
.and()
.oauth2ResourceServer()
.jwt();
}
}
This code defines a basic authorization server and a resource server. But, despite the configuration, the resource server isn't making any calls to the authorization server at startup.
The Solution: Delayed Initialization
The reason for this behavior lies in the way Spring Security OAuth2 handles resource server configuration. The resource server isn't designed to proactively fetch authorization server metadata during startup. It only starts fetching it when a request arrives and needs validation.
The Importance of Request-Based Validation
This approach, while seemingly less efficient at first glance, has several advantages:
- Minimizes Startup Time: The resource server can start quickly without waiting for the authorization server to respond.
- Dynamic Configuration: The authorization server's configuration can change dynamically without restarting the resource server.
- Centralized Validation: The authorization server becomes the single point of truth for validating JWTs, ensuring consistency across all resource servers.
Providing Early Access
If you need to access authorization server information right at startup, you can implement custom initialization logic:
@Configuration
@EnableResourceServer
public class ResourceServerConfig extends ResourceServerConfigurerAdapter {
@Autowired
private JwtDecoder jwtDecoder;
@Override
public void configure(HttpSecurity http) throws Exception {
// ... other configuration ...
}
@PostConstruct
public void init() {
// Fetch authorization server metadata here
// e.g., using a custom OAuth2 client
// Use the fetched metadata to configure the jwtDecoder
// e.g., jwtDecoder.setIssuerUri(issuerUri);
}
}
This example uses the @PostConstruct annotation to trigger a method after the bean has been initialized. In this method, you can fetch metadata from the authorization server and configure your JWT decoder.
Conclusion
While it may seem counterintuitive, the delay in accessing authorization server metadata during startup is an intentional design choice in Spring Security OAuth2. This ensures efficient resource server operation and allows for dynamic configuration changes. By understanding this behavior, you can avoid unnecessary troubleshooting and implement custom logic for scenarios where early access to authorization server information is crucial.
References
- Spring Security OAuth2 Documentation: https://spring.io/guides/tutorials/spring-boot-oauth2/
- JWT Specification: https://www.rfc-editor.org/rfc/rfc7519
