Allow using service account credential for per_rpc_creds interop test.
diff --git a/doc/interop-test-descriptions.md b/doc/interop-test-descriptions.md
index ddeee66..adbfc87 100644
--- a/doc/interop-test-descriptions.md
+++ b/doc/interop-test-descriptions.md
@@ -598,7 +598,7 @@
Similar to the other auth tests, this test is only for cloud-to-prod path.
-This test verifies unary calls succeed in sending messages using a JWT
+This test verifies unary calls succeed in sending messages using a JWT or a service account
credentials set on the RPC.
The test
@@ -606,6 +606,10 @@
downloaded from https://console.developers.google.com. Alternately, if using a
usable auth implementation, it may specify the file location in the environment
variable GOOGLE_APPLICATION_CREDENTIALS
+- optionally uses the flag `--oauth_scope` for the oauth scope if implementator
+wishes to use service account credential instead of JWT credential. For testing
+against grpc-test.sandbox.google.com, oauth scope
+"https://www.googleapis.com/auth/xapi.zoo" should be used.
Server features:
* [UnaryCall][]