OAuth2 REST Client Support in Spring Security 6.4: A New Era of Simplified Configuration

Spring Security 6.4 introduces major improvements in OAuth2 client configuration, particularly with its new RestClient support. This update brings simplified configuration patterns and better alignment between servlet and reactive applications. Let’s dive into what this means for Spring developers.
The Evolution of OAuth2 Client Configuration
Spring Security’s journey through versions 6.2 and 6.3 has been marked by steady improvements in OAuth2 Client configuration. The framework now allows developers to publish beans that are automatically incorporated into the OAuth2 Client configuration during startup. Key improvements include:
- Extension grant types via
OAuth2AuthorizedClientProvider
beans - Custom OAuth2 Access Token Request parameters through
OAuth2AccessTokenResponseClient
beans - Automatic publication of
OAuth2AuthorizedClientManager
beans
Enter RestClient: A Game-Changing Addition
Spring Framework 6.1 introduced RestClient, a synchronous HTTP client with a fluent API similar to WebClient. The key difference? RestClient doesn’t depend on reactive libraries, making it a perfect fit for traditional servlet-based applications.
Why RestClient Matters
- Simplified Configuration: No additional reactive dependencies required
- Familiar API: Similar to WebClient, reducing the learning curve
- Synchronous Operations: Better suited for traditional servlet applications
- Unified Approach: Aligns servlet and reactive stacks on a common configuration model
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Implementing OAuth2 with RestClient
Here’s how to set up protected resource requests using RestClient:
First, add the required dependency:
implementation 'org.springframework.boot:spring-boot-starter-oauth2-client'
Configure your client registration:
spring:
security:
oauth2:
client:
registration:
messaging-client:
provider: spring
client-id: client1
client-secret: my-secret
authorization-grant-type: authorization_code
scope: message.read,message.write
provider:
spring:
issuer-uri: http://localhost:9000
Set up RestClient configuration:
@Configuration
public class RestClientConfig {
@Bean
public RestClient restClient(RestClient.Builder builder,
OAuth2AuthorizedClientManager authorizedClientManager) {
OAuth2ClientHttpRequestInterceptor requestInterceptor =
new OAuth2ClientHttpRequestInterceptor(authorizedClientManager);
return builder.requestInterceptor(requestInterceptor).build();
}
}
Advanced Features and Customizations
Parameter Customization
Spring Security 6.4 introduces powerful features for customizing OAuth2 Access Token requests:
- Parameter Override: Use
setParametersConverter()
to modify default parameters - Parameter Omission: Utilize
setParametersCustomizer()
to remove unwanted parameters
Example for omitting client_id when using client assertions:
@Configuration
@EnableWebFluxSecurity
public class SecurityConfig {
@Bean
public ReactiveOAuth2AccessTokenResponseClient<OAuth2ClientCredentialsGrantRequest>
clientCredentialsAccessTokenResponseClient() {
WebClientReactiveClientCredentialsTokenResponseClient client =
new WebClientReactiveClientCredentialsTokenResponseClient();
client.setParametersCustomizer((parameters) -> {
if (parameters.containsKey(OAuth2ParameterNames.CLIENT_ASSERTION)) {
parameters.remove(OAuth2ParameterNames.CLIENT_ID);
}
});
return client;
}
}
Migration Path
For teams using RestTemplate, Spring Security 6.4 provides a smooth migration path:
- Convert existing RestTemplate to RestClient using
RestClient.create(RestTemplate)
- Align configuration patterns with the reactive stack
- Prepare for Spring Security 7.0’s unified configuration model
Key Takeaways
- Simplified Configuration: RestClient support reduces boilerplate and complexity
- Better Integration: Seamless integration between servlet and reactive applications
- Enhanced Customization: Greater control over OAuth2 Access Token requests
- Future-Ready: Alignment with Spring Security’s future direction
Looking Forward
Spring Security 6.4’s RestClient support represents a significant step toward simplifying OAuth2 configuration while maintaining flexibility. Whether you’re building a new application or maintaining an existing one, these improvements offer clearer, more consistent ways to handle OAuth2 authentication and authorization.
The release is currently available as version 6.4.0-RC1, providing an excellent opportunity for developers to test these features and provide feedback to the Spring Security team.
For developers looking to get started, the Spring Security reference documentation and sample applications provide comprehensive guides and examples. The alignment between servlet and reactive stacks makes this an ideal time to standardize OAuth2 configuration patterns across your Spring applications.