diff --git a/lib/base_service.ts b/lib/base_service.ts
index 18c649e22..bf654f219 100644
--- a/lib/base_service.ts
+++ b/lib/base_service.ts
@@ -46,6 +46,8 @@ export interface UserOptions {
   iam_client_secret?: string;
   authentication_type?: string;
   disable_ssl_verification?: boolean;
+  /** Allow additional request config parameters */
+  [propName: string]: any;
 }
 
 export interface BaseServiceOptions extends UserOptions {