Passkey is some sort of specific unique key to a device allowing to use a pin on a device instead of the password. But which won’t work on another device.
Now I don’t know if that key can be stolen or not, or if it’s really more secure or not, as people have really unsecure pins.
I’m not sure if this is universal or specific to the last site I tried to use my Yubikey with as a passkey, but it only would allow it to be used as 2FA, not actual passwordless authentication.
I assume this is because Yubikeys don’t create a secret for each individual website I suppose? Not exactly sure about that one.
Both the website and your physical security token must support the right type of webauthn credentials (the token has storage for a certain number of slots with “discoverable credentials”).
Passkeys is a variant of the same which is bound to your device’s own TPM / SE security chip or equivalent, plus a synchronization feature for backups.
You can use Yubico keys as your passwordless logins. Both Google and Microsoft have this option.
Strangely enough, Google lets me “add” my Yubikey as a passkey, but then does not let me sign in with it due to it not being “recognized”. If I remove it as a passkey, and only use it as a 2FA token, attempt to sign in and use the “Enter your password” option, it will then let me use the key after I’ve entered my password as a second factor.
So it seems Google has removed the error (or its not triggering anymore) as they will have been one of the first sites I tried to create a passkey for, but it still does not let you use it as a passkey.
I haven’t encountered this issue, yet. I’m using LibreWolf browser (v118.0) and tested logging in my Google and MS account passwordless. BTW, I have Yubico Security Key NFC (the blue one).