add test for vertex basic pass throgh

litellm/proxy/example_config_yaml/custom_auth_basic.py

@@ -0,0 +1,14 @@
+from fastapi import Request
+
+from litellm.proxy._types import UserAPIKeyAuth
+
+
+async def user_api_key_auth(request: Request, api_key: str) -> UserAPIKeyAuth:
+    try:
+        return UserAPIKeyAuth(
+            api_key="best-api-key-ever",
+            user_id="best-user-id-ever",
+            team_id="best-team-id-ever",
+        )
+    except:
+        raise Exception