Here [1] is Yubico's draft WebAuthn recovery ("backup authenticator") extension spec, which is possibly what you're thinking of. [1] https://github.com/Yubico/

Here [1] is Yubico's draft WebAuthn recovery ("backup authenticator") extension spec, which is possibly what you're thinking of. [1] https://github.com/Yubico/webauthn-recovery-extension https://github.com/Yubico/webauthn-recovery-extension