make C# auth interop tests up to spec
diff --git a/tools/run_tests/run_interop_tests.py b/tools/run_tests/run_interop_tests.py
index 45efa57..c1b4cf8 100755
--- a/tools/run_tests/run_interop_tests.py
+++ b/tools/run_tests/run_interop_tests.py
@@ -312,6 +312,10 @@
if test_case in ['per_rpc_creds', 'oauth2_auth_token']:
cmdline += [oauth_scope_arg]
+ if test_case == 'oauth2_auth_token' and language == 'c++':
+ # C++ oauth2 test uses GCE creds and thus needs to know the default account
+ cmdline += [default_account_arg]
+
if test_case == 'compute_engine_creds':
cmdline += [oauth_scope_arg, default_account_arg]