Related to this question: 

^ Zapier doesn’t seem to support updating just documents in Firestore, only Firebase (doesn’t make much sense to me as to why) and because of that, I need to write a custom webhook to do the update. That step in my zap makes sense and should work fine. However, before that can happen I need to authenticate and get a bearer (oauth) token to then authorize that PATCH request, but I can’t figure out how to do this within the context of a zap.

All Google docs point to needing a running web server environment of some kind so you can execute the gloud CLI, or use custom code to generate a JWT which obviously isn’t possible here (and I’d prefer not to standup a cloud function to call out to, etc).

So I guess the question is: I’d like to, within the context of a Zapier Webhook (so some kind of HTTP request), get an oauth token for a service account I have in GCP so I can authorize my Cloud Firestore REST API request. Is that possible given Google’s current REST APIs and what they require to generate a token?