Overview:

Trying to use TouchID for WebAuthN does not work. I have narrowed it down to the "attestation" parameter being set. If it is not set, it works.

Steps to Reproduce: 

1) Go to https://webauthn.io 
2) Enter anything on example_username
3) Change the dropdown for attestation to either direct or indirect. 
4) Click register. Click Continue in the prompt "Do you want to save a passkey for X"
5) Touch the fingerprint sensor when asked

Actual Result: Error stating "The operation cannot be completed."

Expected: Successfully registering.
 
In Safari 15.4 it will also fail similarly, but it will fail in a worse way where the whole browser window is unusable and must be force killed.

If I skip step 3 and leave attestation at "none". Things will work as expected.