We had originally planned to go all-in on passkeys for ONCE/Campfire, and we built the early authentication system entirely around that. It was not a simple setup! Handling passkeys properly is surprisingly complicated on the backend, but we got it done. Unfortunately, the user experience kinda sucked, so we ended up ripping it all out...
I just wish that companies enabling passkeys would still allow password+MFA. There are several sites that, when you enable passkeys, lock you out of MFA for devices that lack a biometric second factor of authentication. I’d love to use passkeys + biometrics otherwise, since I’ve often felt that the auth problem would be best solved with asymmetric cryptography.