diff --git a/tests/v1beta3/authconfig.yaml b/tests/v1beta3/authconfig.yaml
index 2c7e4430..509b93fe 100644
--- a/tests/v1beta3/authconfig.yaml
+++ b/tests/v1beta3/authconfig.yaml
@@ -39,7 +39,7 @@ spec:
         roles:
           expression: auth.identity.realm_access.roles
         username:
-          expression: auth.identity["preferred_username"]
+          expression: "has(auth.identity.preferred_username) ? auth.identity.preferred_username : 'unknown'"
     oauth2-introspection:
       oauth2Introspection:
         credentialsRef:
@@ -55,7 +55,7 @@ spec:
         roles:
           expression: auth.identity.realm_access.roles
         username:
-          expression: auth.identity["preferred_username"]
+          expression: "has(auth.identity.preferred_username) ? auth.identity.preferred_username : 'unknown'"
       cache:
         key:
           expression: request.headers["authorization"]