How do I add a custom domain redirect to this auth?

I am trying to follow option 1 of the redirect best practices from firebase:
https://firebase.google.com/docs/auth/web/redirect-best-practices

Start by reading Firebase's redirect best practices linked in the issue, then inspect how this React wrapper exposes Firebase Authentication redirects. The payload names no repository file or test; clarify the expected custom-domain behavior and define a test or concrete completion condition before starting.

Written by the indexing model from the issue text.