Also along these lines, there's a really neat little library called "SimpleWebAuthn" that also supports Passkeys, and is basically a small dependency-free set of client Javascript (for initiating the user flow) and a small JavaScript server component to go with it: https://simplewebauthn.dev/

The code is pretty simple and a good place to start, as well as AuthCompation, if you wanted to roll your own library in your language of choice or whatever, or something very custom. I found both useful recently.