Face ID and Touch ID for the Web (2020)
You can use Face ID or Touch ID on your own website to authenticate users! The flow in the video seems easy and stratight forward from a user perspective.
A quite good introduction video by Jiewen Tan, speaking at Apple's WWDC 2020: https://developer.apple.com/videos/play/wwdc2020/10670/ (~16 minutes)
Blog post with the same material: https://webkit.org/blog/11312/meet-face-id-and-touch-id-for-the-web/
If you use this on your phone you can see some of it in action: https://webauthn.me/debugger
This came up about 12 months ago on HN https://news.ycombinator.com/item?id=23631518