External Collection - Firebase - how to set-up authentication and query

Hello Adalo community

I am having a hard time to create a Firebase (Firestore specifically) External Collection (EC).
After many attempts, I think I will have to create two EC, one for authentication (where it generates an “access code”) and one for the REST query.

Can anyone share a few highlight about this?
Can anyone share things like:

  • how the authentication should be create in EC?
  • which kind of URI redirect to use?
  • how to manage access token expiration?

Any help is very welcome.

Thanks a lot