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.
Google definitely supports passkeys, and they were one of the sites that did this. I’ve just replied to another comment regarding this. I wonder if the Yubikey 4 (I’m not sure how to tell which one I have, since they look about the same) just doesn’t support passkeys, which would be… unfortunate.
It’ll be even more unfortunate if there’s a weird mix of sites that support the Yubikey as a passkey and some only support it as a passkey. My Pixel is supported as a passkey, but Firefox on Linux doesn’t support this - only on Windows and macOS. I believe Chrome/Chromium does, which is equally as frustrating as my Yubikey possibly not supporting passkeys.
Per Yubico’s specs on the Yubikey 4, it does not support FIDO 2 resident credentials, meaning it does not support Passkeys.
Compare to the specs of the Yubikey 5C NFC or Yubico Security Key C NFC, which both have this section:
See also Yubico blog post with an FAQ about passkeys:
I wouldn’t run out right now and buy a Yubikey to store Passkeys given the 25 key limit and the likelihood that Yubico releases a new key that supports storing far more of them, but if you do, the $25 Security Key series is the cheapest option.
The credential needs to be set as discoverable and some other stuff to work for passwordless login (the token must store site specific data)
You would need to reregister it as passwordless to not just use it as 2FA after having entered a password (meanwhile standard 2FA with webauthn don’t store anything on the token, the website sends encrypted credentials to the token which only the token can decrypt and then authenticate with)