Add RequestDecorator to allow SDK clients to modify the request

impl/http/src/main/java/io/serverlessworkflow/impl/executors/http/HttpExecutor.java

@@ -24,9 +24,11 @@
 import jakarta.ws.rs.client.Invocation.Builder;
 import jakarta.ws.rs.client.WebTarget;
 import java.net.URI;
+import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Optional;
+import java.util.ServiceLoader;
 import java.util.concurrent.CompletableFuture;
 
 public class HttpExecutor implements CallableTask {
@@ -36,6 +38,7 @@ public class HttpExecutor implements CallableTask {
   private final Optional<WorkflowValueResolver<Map<String, Object>>> headersMap;
   private final Optional<WorkflowValueResolver<Map<String, Object>>> queryMap;
   private final RequestExecutor requestFunction;
+  private final List<RequestDecorator> requestDecorators;
 
   HttpExecutor(
       WorkflowValueResolver<URI> uriSupplier,
@@ -48,6 +51,11 @@ public class HttpExecutor implements CallableTask {
     this.queryMap = queryMap;
     this.requestFunction = requestFunction;
     this.pathSupplier = pathSupplier;
+    this.requestDecorators =
+        ServiceLoader.load(RequestDecorator.class).stream()
+            .map(ServiceLoader.Provider::get)
+            .sorted()
+            .toList();
   }
 
   public CompletableFuture<WorkflowModel> apply(
@@ -67,6 +75,11 @@ public CompletableFuture<WorkflowModel> apply(
       target = target.queryParam(entry.getKey(), entry.getValue());
     }
     Builder request = target.request();
+
+    for (RequestDecorator requestDecorator : requestDecorators) {
+      requestDecorator.decorate(request, workflow, taskContext, input);
+    }
+
     headersMap.ifPresent(
         h -> h.apply(workflow, taskContext, input).forEach((k, v) -> request.header(k, v)));
     return CompletableFuture.supplyAsync(

impl/http/src/main/java/io/serverlessworkflow/impl/executors/http/RequestDecorator.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2020-Present The Serverless Workflow Specification Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.serverlessworkflow.impl.executors.http;
+
+import io.serverlessworkflow.impl.ServicePriority;
+import io.serverlessworkflow.impl.TaskContext;
+import io.serverlessworkflow.impl.WorkflowContext;
+import io.serverlessworkflow.impl.WorkflowModel;
+import jakarta.ws.rs.client.Invocation;
+
+/**
+ * Interface for decorating HTTP requests with additional modifications.
+ *
+ * <p>Implementations should be loaded via ServiceLoader and are sorted by priority in ascending
+ * order (lower priority numbers executed first). Decorators are applied in sequence, where later
+ * decorators can override headers set by earlier decorators with the same header name.
+ *
+ * @see ServicePriority
+ */
+public interface RequestDecorator extends ServicePriority {
+
+  /**
+   * Decorate the HTTP request builder with additional headers or modifications.
+   *
+   * @param requestBuilder the request builder to decorate
+   * @param workflowContext the workflow context
+   * @param taskContext the task context
+   * @param workflowModel the input data
+   */
+  void decorate(
+      Invocation.Builder requestBuilder,
+      WorkflowContext workflowContext,
+      TaskContext taskContext,
+      WorkflowModel workflowModel);
+}