Support arbitrary requests

[andresespinosapc]

It's very difficult to find the classes needed to make a request, so at least you should provide a method to make any request but taking advantage of the authentication from the library.

Another option that would work for me is to use raw requests, but I don't find the documentation on how to authenticate using service accounts. The one I found only works with the library: https://cloud.google.com/docs/authentication/production

[dazuma]

I suspect the best way forward is to include appropriate documentation and/or code in the googleauth gem, so that you can attach Google credentials to any http request as you suggest. I'm going to transfer this issue over there for tracking.