rustlavel-webauthn: passkeys, written on the W3C WebAuthn specification.
A password is a shared secret: the server holds something that can be stolen from it, and the user types something that can be phished out of them. A passkey is neither. The authenticator keeps a private key that never leaves it, the server stores only the public half, and the signature covers the origin — so a convincing copy of your login page at a different address gets nothing, because the browser will not sign for it.
That last property is the one worth the work. Every other second factor can be relayed by a good enough phishing page; this one cannot.
Everything here is written from scratch except the signature verification. CBOR, COSE framing, the ceremonies, the challenge handling — all ours. The elliptic-curve maths is not, and should not be: a subtly wrong verifier accepts forged assertions, which is the single failure this package exists to prevent.