sync messages.proto up to date.

test/cpp/interop/messages.proto

@@ -36,6 +36,12 @@ message SimpleRequest {
 
   // Optional input payload sent along with the request.
   optional Payload payload = 3;
+
+  // Whether SimpleResponse should include username.
+  optional bool fill_username = 4;
+
+  // Whether SimpleResponse should include OAuth scope.
+  optional bool fill_oauth_scope = 5;
 }
 
 // Unary response, as configured by the request.
@@ -44,7 +50,9 @@ message SimpleResponse {
   optional Payload payload = 1;
   // The user the request came from, for verifying authentication was
   // successful when the client expected it.
-  optional int64 effective_gaia_user_id = 2;
+  optional string username = 2;
+  // OAuth scope.
+  optional string oauth_scope = 3;
 }
 
 // Client-streaming request.