Play Games Services Server-Side API Access sample

I'm trying to implement the Java example [shown here](https://developers.google.com/games/services/android/offline-access#exchange_the_server_auth_code_for_an_access_token_on_the_server) with Nodejs using the client libraries. My server runs as a Cloud Run Service. I've tried several variations of the samples shown here, but they all ended up `Invalid Credentials` error.

Required credentials are all set up in Play Console, the Android client can login to Games Services, can get the authCode [as shown here](https://developers.google.com/games/services/android/offline-access#get_the_server_auth_code), pass that code to server, and I could not figure out how to proceed after that. I just want to verify this player on the server, calling `applications.verify()` method.