Firebase Auth is my go-to, but I don't consider myself an expert as I only work with TypeScript and React/Nextjs. I still have to do some hands on work managing the user session, and relating users to other related records in Firestore. And their prebuilt UI components can be problematic. And of course I have to keep user data in sync with payment state by handling Stripe events.

I'd love to find something even more hands-off for my next project...