RFC: Project ID Detection

[bshaffer]

Adds Project ID Detection in this order:

• Project ID from Application Default Credentials
• Project ID from GCLOUD_CONFIG environment variable
• Project ID from App Engine AppIdentity service
• Project ID from Compute Engine metadata server
• Project ID from gcloud default config file

As "Project ID" is only used for API calls to Google Cloud Platform, it makes more sense to put this in google/cloud as opposed to google/auth

[stephenplusplus]

I'm not sure if this makes a difference, but for Node, this logic went into the auth library (PR). Exposing this detection in a lower level for more libraries to take advantage of would probably be well received.

The other languages were going to put this behavior in the auth layer as well, though I haven't followed their conversations to confirm.

[dwsupplee]

I agree with @stephenplusplus that I could see there being value in detecting the project ID from the auth layer.

Adding on to your point, it does look like ruby plans to add the same support to the auth library as well: googleapis/google-auth-library-ruby#90.

@bshaffer do you think given that we should follow suit?

[bshaffer]

We are having this conversation and trying to decide where best to place this. Since project ID is only used in cloud-based APIs, I am of the opinion it should be implemented here.

[jdpedrie]

I don't know if I agree with that @bshaffer. There may not be many first-party libraries that need to determine project IDs, but there are some (the work done by @tomwalder comes to mind) that do interact with the cloud APIs and thus need project IDs. Surely more will come as time goes on, to fill in gaps which google-cloud-php doesn't cover. Easing project ID detection would surely make things simpler for more than just us. 😄

[tomwalder]

Hey. It would certainly cause some problems for the PHP-GDS library if project ID detection got moved into this library.

What about a distinct library for Project ID detection, which can then be composed in?

e.g. google/google-cloud-project-detect-php

Or something less catchy? :)

[bshaffer]

@tomwalder I would prefer to keep things simple if possible. The consensus is in resounding favor of moving this to google/auth, and @jdpedrie brings up a good point.

[bshaffer]

closing because this will never ever be merged ever