So happy Apple decided to go with an open standard here rather than something proprietary. This is good news for the FIDO2 ecosystem and I hope this leads to far greater support for FIDO2 authenticators of all types. There is another world in which Apple just pushed 'Sign in with Apple' and created yet another federated identity provider rather than true, 'secure element'-based FIDO2 authentication.
It feels like a little like the first day we start to understand how "Big Tent" (in the OpenStack sense) FIDO2 ecosystem is. You can do whatever, make anything, and call it FIDO2; it's all duck typing: looks like a duck, quacks must be a duck. No implementation details are required, no transparency is needed, everything can be totally vendored way way up, and the standard will welcome you. Your platform is welcome here. This post is about how to use & prefer that platform, over the more common means available.
For sure this is overwhelmingly a good thing. It's by design that we allow platform authenticators in WebAuthn. Apple is allowing their closed, proprietary security technologies to seamlessly work on the web without making webdevs jump through hoops. It's a good thing, and this will really help Web Authentication for sure.
Still I have some wistfulness. It's a good user experience, it's great. It's a win for devs, it's a win for users. Still there's some larger context I can't quite put my finger on, when I see "authenticatorSelection: { authenticatorAttachment: "platform" }". The web is letting more of the native platform shine through, and that's good, but it also forgoes some of the knowability & commonality that resounds on so much of the rest of the web, and while the immediate impact is extremely good, I still think there's some kind of hard to describe ultra-slow-motion civilization-scale loss that's also passenger to this successful commingling of web and platform.