feat: add operation authorization forward middleware

app/controlplane/api/controlplane/v1/operation_authorization.proto

@@ -0,0 +1,41 @@
+//
+// Copyright 2026 The Chainloop 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.
+
+syntax = "proto3";
+
+package controlplane.v1;
+
+option go_package = "github.com/chainloop-dev/chainloop/app/controlplane/api/controlplane/v1;v1";
+
+// OperationAuthorizationService is implemented by an external service
+// to authorize specific control plane operations.
+service OperationAuthorizationService {
+  rpc Check(OperationAuthorizationServiceCheckRequest) returns (OperationAuthorizationServiceCheckResponse);
+}
+
+message OperationAuthorizationServiceCheckRequest {
+  // The gRPC operation being authorized, e.g. "/controlplane.v1.OrganizationService/Create"
+  string operation = 1;
+  // The user ID requesting the operation
+  string user_id = 2;
+  // The organization ID in context, if any
+  string organization_id = 3;
+}
+
+message OperationAuthorizationServiceCheckResponse {
+  bool allowed = 1;
+  // Human-readable reason when denied
+  string reason = 2;
+}