I have a mobile app that has data & auth on Firebase. I want to create a Google Action for these same users.
This post asked basically the same question and the top reply says "However, you can use Firebase Auth if you're willing to setup your own OAuth2 server. If you set one up you can have them login using Firebase Sign-In, generate the token and store it against their Firebase ID, and issue that token to the Assistant client. When you get that token back, you can easily associate it back to the Firebase ID."
Does anybody have an example or a more in depth guideline of how to accomplish this?