How Hype (Passkeys) Will Turn Your Security Key Into Junk

tl;dr: passkeys, as proposed now, will fill up existing fido2/webauthn authenticators if the feature becomes widespread enough. this is because the feature of "passkeys" actually refer to resident keys, which most authenticators today can only store a limited amount of (some, none at all!). preventing this will require changes to either webauth, fido, or passkey libraries.