Let's say I have a new account and a single Passkey in the TPM of PC1. I want to log in from PC2, too. How can I do that? (I know there is some trickery with Bluetooth, but I haven't seen anything supporting it, and desktop PCs usually doesn't have Bluetooth connectivity.)
AFAIK some browsers can do some magic to use a Passkey from your smartphone on a PC, but you need to log in to the same browser-sync account from both device (which brings back us to the same issue).
Also the whole thing becomes a mess when you change devices. You need to log into all the services you have ever used to delete the Passkeys from devices you no longer have, and you need to add a new passkey from a new device you bought to all the services you use.
If you don't want to downgrade security, how about requiring confirmation from another session that is already logged in using a passkey? e.g. You try to log in on PC2. A prompt appears with something like "confirm this login from [PC1, etc.]". You log in on PC1 using your passkey. The service recognizes that the login id definitely you, or at least someone in possession of your physical device and login method for that device. Therefore, it then allows PC2 to register a new passkey. Kinda similar to how google confirms new logins by sending a notification to your phone.
How can I do that, if Passkeys are the only option to log in?
If I can just use a password to log into a website without Passkeys, then Passkey is useless and doesn't add any security benefit.
> Why would you need to delete invalid passkeys? You wouldn't.
I sell my old (and no longer updated) phone or PC and don't want someone to get access to my account by getting access to the secret keys.
An non-revocable authentication mechanism is just stupid.
That's the real failure? I think the real failure is that people must have _more than one_. I thought so hard to add all my credentials to 1Password. Now people tell me I should use a Yubikey (or better two or three of them). What do you think, I'm going to register a couple of hundred accounts times three for something I already have (my password manager)?
The real advante in passkeys is in allowing me to log in into a service on a foreign device without typing [my password], which is (honestly) something now sane person should ever do.