Congrats on WebAuthn support! Interesting to see you rolled your own solution instead of using the webauthn gem, if there’s any feedback for us there I’d love to hear it 
I noticed in your implementation only supports algorithm -7 (ES256), but Windows Hello platform authenticators (backed by TPM 2.0 hardware) require -257 (RS256) as per Microsoft’s documentation. TPM 2.0 is required since July 28, 2016 for new Windows 10 desktop models, so that’s not an insignificant amount of hardware.
One suggestion for the “Login Flow” mockup - WebAuthn has an official logo that could be used instead of a generic fingerprint image. Besides fingerprint, facial recognition, swipe pattern or PIN are common user verification options as well.