feat: [iap] add oauth fields for IapSettings

packages/google-cloud-iap/protos/google/cloud/iap/v1/service.proto

@@ -1,4 +1,4 @@
-// Copyright 2025 Google LLC
+// Copyright 2026 Google LLC
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -484,6 +484,23 @@ message OAuthSettings {
   // since access behavior is managed by IAM policies.
   google.protobuf.StringValue login_hint = 2;
 
+  // Optional. OAuth 2.0 client ID used in the OAuth flow.
+  // This allows for client sharing. The risks of client sharing
+  // are outlined here:
+  // https://cloud.google.com/iap/docs/sharing-oauth-clients#risks.
+  google.protobuf.StringValue client_id = 3
+      [(google.api.field_behavior) = OPTIONAL];
+
+  // Optional. Input only. OAuth secret paired with client ID.
+  google.protobuf.StringValue client_secret = 4 [
+    (google.api.field_behavior) = INPUT_ONLY,
+    (google.api.field_behavior) = OPTIONAL
+  ];
+
+  // Output only. OAuth secret SHA256 paired with client ID.
+  google.protobuf.StringValue client_secret_sha256 = 6
+      [(google.api.field_behavior) = OUTPUT_ONLY];
+
   // Optional. List of client ids allowed to use IAP programmatically.
   repeated string programmatic_clients = 5
       [(google.api.field_behavior) = OPTIONAL];