SITUATION:
I follow this tutorial: https://cloud.google.com/nodejs/tutorials/bookshelf-on-compute-engine
Everything works fine until I do
If you're running the app locally, then the gcloud beta auth application-default login command should suffice for acquiring local credentials (I updated the tutorial to say so).
When running the app on Google Compute Engine, if the Compute Engine instance was created with the proper scopes (cloud-platform should be sufficient) then the app will authenticate with Google Cloud Platform APIs automatically without any extra work on your part.