feat: Add OAuth2 proxy support using JVM system properties

Simplify OAuth2 authentication to automatically respect JVM proxy settings
(e.g., -Dhttps.proxyHost, -Dhttps.proxyPort). The implementation uses Reactor
Netty's built-in proxyWithSystemProperties() method, which gracefully handles
both proxy and non-proxy scenarios without additional configuration.

Author: joshuaNathaniel

api/src/main/java/io/kafbat/ui/config/auth/OAuthSecurityConfig.java

@@ -11,15 +11,14 @@
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import org.jetbrains.annotations.Nullable;
-import org.springframework.beans.factory.annotation.Autowired;
-import org.springframework.beans.factory.annotation.Qualifier;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.boot.autoconfigure.security.oauth2.client.OAuth2ClientProperties;
 import org.springframework.boot.autoconfigure.security.oauth2.client.OAuth2ClientPropertiesMapper;
 import org.springframework.boot.autoconfigure.security.oauth2.resource.OAuth2ResourceServerProperties;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.http.client.reactive.ReactorClientHttpConnector;
 import org.springframework.security.config.Customizer;
 import org.springframework.security.config.annotation.method.configuration.EnableReactiveMethodSecurity;
 import org.springframework.security.config.annotation.web.reactive.EnableWebFluxSecurity;
@@ -40,6 +39,7 @@
 import org.springframework.security.web.server.authentication.logout.ServerLogoutSuccessHandler;
 import org.springframework.web.reactive.function.client.WebClient;
 import reactor.core.publisher.Mono;
+import reactor.netty.http.client.HttpClient;
 
 @Configuration
 @ConditionalOnProperty(value = "auth.type", havingValue = "OAUTH2")
@@ -92,7 +92,6 @@ public ReactiveOAuth2UserService<OidcUserRequest, OidcUser> customOidcUserServic
       ReactiveOAuth2UserService<OAuth2UserRequest, OAuth2User> oauth2UserService) {
     final OidcReactiveOAuth2UserService delegate = new OidcReactiveOAuth2UserService();
 
-    // Use our custom OAuth2 user service which may have proxy support
     delegate.setOauth2UserService(oauth2UserService);
 
     return request -> delegate.loadUser(request)
@@ -109,16 +108,15 @@ public ReactiveOAuth2UserService<OidcUserRequest, OidcUser> customOidcUserServic
   }
 
   @Bean
-  public ReactiveOAuth2UserService<OAuth2UserRequest, OAuth2User> customOauth2UserService(
-      AccessControlService acs,
-      @Autowired(required = false) @Qualifier("oauth2WebClient") WebClient oauth2WebClient) {
+  public ReactiveOAuth2UserService<OAuth2UserRequest, OAuth2User> customOauth2UserService(AccessControlService acs) {
     final DefaultReactiveOAuth2UserService delegate = new DefaultReactiveOAuth2UserService();
 
-    // If proxy-configured WebClient is available, use it
-    if (oauth2WebClient != null) {
-      delegate.setWebClient(oauth2WebClient);
-      log.debug("OAuth2 user service configured with custom WebClient (proxy support)");
-    }
+    // Configure WebClient to use system proxy properties (if set)
+    delegate.setWebClient(
+        WebClient.builder()
+            .clientConnector(new ReactorClientHttpConnector(
+                HttpClient.create().proxyWithSystemProperties()))
+            .build());
 
     return request -> delegate.loadUser(request)
         .flatMap(user -> {