Email-less and password-less registration & authentication

[Be0 (Be)]

@Be0

However, this would create a usability problem for authentication on new devices because users wouldn’t have the FIDO platform authenticator available on a new device and relying solely on the password to setup a new device wouldn’t be secure. To resolve this, I propose a workflow similar to how Matrix authenticates new clients. The user could try to login on a new device with that device’s FIDO platform authenticator (a new factor) and their password (an already registered factor). This would not actually log in, but it would create a request to approve the new FIDO authenticator in the account. The UI on the new device would then direct the user to log in on a device they already have registered to approve the new device. With FIDO platform authenticators built into mobile devices, this could be practically usable for secure authentication without specialized roaming authenticator hardware or sacrificing the ability to use any ad-hoc device like a public kiosk.

Looks like Google has come up with an interesting solution for this using QR codes and Bluetooth:

Android solutions for seamless sign-in across devices

Passkeys.io – A Real-World Passkey Demo & Info Page