refactor: Move @ClientRegistrationId annotation to class level

Move the @ClientRegistrationId annotation from individual methods to the
interface class level, following Spring Security's recommended practice.

Changes:
- Update api.mustache to place annotation on interface declaration
- Modify SpringCodegen to set clientRegistrationId on operations map
- Update sample code to show class-level annotation
- Update README with improved example and explanation

This approach is cleaner and avoids repeating the annotation on every method,
as recommended in Spring Security documentation.

Author: claude

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/SpringCodegen.java

@@ -871,11 +871,6 @@ public void setIsVoid(boolean isVoid) {
 
                 prepareVersioningParameters(ops);
                 handleImplicitHeaders(operation);
-
-                // Add clientRegistrationId for spring-http-interface with OAuth
-                if (SPRING_HTTP_INTERFACE.equals(library) && clientRegistrationId != null && !clientRegistrationId.isEmpty()) {
-                    operation.vendorExtensions.put("clientRegistrationId", clientRegistrationId);
-                }
             }
             // The tag for the controller is the first tag of the first operation
             final CodegenOperation firstOperation = ops.get(0);
@@ -884,6 +879,11 @@ public void setIsVoid(boolean isVoid) {
             // But use a sensible tag name if there is none
             objs.put("tagName", "default".equals(firstTagName) ? firstOperation.baseName : firstTagName);
             objs.put("tagDescription", escapeText(firstTag.getDescription()));
+
+            // Add clientRegistrationId for spring-http-interface with OAuth
+            if (SPRING_HTTP_INTERFACE.equals(library) && clientRegistrationId != null && !clientRegistrationId.isEmpty()) {
+                operations.put("clientRegistrationId", clientRegistrationId);
+            }
         }
 
         removeImport(objs, "java.util.List");

modules/openapi-generator/src/main/resources/JavaSpring/libraries/spring-http-interface/api.mustache

@@ -15,9 +15,9 @@ import org.springframework.http.ResponseEntity;
 {{/useResponseEntity}}
 import org.springframework.web.bind.annotation.*;
 import org.springframework.web.service.annotation.*;
-{{#operations}}{{#operation}}{{#vendorExtensions.clientRegistrationId}}
+{{#operations}}{{#clientRegistrationId}}
 import org.springframework.security.oauth2.client.annotation.ClientRegistrationId;
-{{/vendorExtensions.clientRegistrationId}}{{/operation}}{{/operations}}
+{{/clientRegistrationId}}{{/operations}}
 import org.springframework.web.multipart.MultipartFile;
 {{#reactive}}
 
@@ -35,6 +35,9 @@ import {{javaxPackage}}.annotation.Generated;
 {{>generatedAnnotation}}
 
 {{#operations}}
+{{#clientRegistrationId}}
+@ClientRegistrationId("{{clientRegistrationId}}")
+{{/clientRegistrationId}}
 public interface {{classname}} {
 {{#operation}}
 
@@ -60,9 +63,6 @@ public interface {{classname}} {
     {{#isDeprecated}}
     @Deprecated
     {{/isDeprecated}}
-    {{#vendorExtensions.clientRegistrationId}}
-    @ClientRegistrationId("{{vendorExtensions.clientRegistrationId}}")
-    {{/vendorExtensions.clientRegistrationId}}
     {{^useResponseEntity}}
     @ResponseStatus({{#springHttpStatus}}{{#responses.0}}{{{code}}}{{/responses.0}}{{/springHttpStatus}})
     {{/useResponseEntity}}

samples/client/petstore/spring-http-interface-oauth/README.md

@@ -30,18 +30,23 @@ openapi-generator-cli generate \
 
 ## Generated Code
 
-The generated interface methods will include the `@ClientRegistrationId` annotation:
+The generated interface will include the `@ClientRegistrationId` annotation at the class level:
 
 ```java
 @ClientRegistrationId("petstore-oauth")
-@HttpExchange(
-    method = "GET",
-    value = "/pet/{petId}",
-    accept = { "application/json" }
-)
-ResponseEntity<PetDto> getPetById(@PathVariable("petId") Long petId);
+public interface PetApi {
+
+    @HttpExchange(
+        method = "GET",
+        value = "/pet/{petId}",
+        accept = { "application/json" }
+    )
+    ResponseEntity<PetDto> getPetById(@PathVariable("petId") Long petId);
+}
 ```
 
+This follows the Spring Security recommendation to add `@ClientRegistrationId` at the type level to avoid repeating the declaration on every method.
+
 ## Spring Security Integration
 
 This annotation is part of Spring Security's OAuth2 integration for HTTP Service Clients. It automatically associates OAuth2 tokens with HTTP requests.

samples/client/petstore/spring-http-interface-oauth/src/main/java/org/openapitools/api/PetApi.java

@@ -20,6 +20,7 @@
 
 @Generated(value = "org.openapitools.codegen.languages.SpringCodegen")
 
+@ClientRegistrationId("petstore-oauth")
 public interface PetApi {
 
     /**
@@ -28,7 +29,6 @@ public interface PetApi {
      * @param petDto Pet object that needs to be added to the store (required)
      * @return successful operation (status code 200)
      */
-    @ClientRegistrationId("petstore-oauth")
     @HttpExchange(
         method = "POST",
         value = "/pet",
@@ -45,7 +45,6 @@ ResponseEntity<Void> addPet(
      * @param petId ID of pet to return (required)
      * @return successful operation (status code 200)
      */
-    @ClientRegistrationId("petstore-oauth")
     @HttpExchange(
         method = "GET",
         value = "/pet/{petId}",
@@ -61,7 +60,6 @@ ResponseEntity<PetDto> getPetById(
      * @param petDto Pet object that needs to be updated in the store (required)
      * @return successful operation (status code 200)
      */
-    @ClientRegistrationId("petstore-oauth")
     @HttpExchange(
         method = "PUT",
         value = "/pet",