Webauthn: add additional attestation format(s) from Apple

[equalsJeffH]

Apple has indicated they have their own attestation statement format(s) that they'd like to have included in the spec. this is just a placeholder to keep it in mind.

[equalsJeffH]

on 2020-08-26 call: jiewan is still awaiting for internal reply, it'll be only one attestation.

[mackie1001]

As of iOS 14 Beta 6 it appears the new attestation format is now in play. Based on conversations you've had is this subject to change or are we just waiting on official documentation?
I see that some have started looking into it using the DeviceCheck/AppAttest docs as a starting point but do you know of any working reference implementations?

[equalsJeffH]

we are waiting apple to provide a specification of their attestation statement format(s)

[mpeng-okta]

Quick question @equalsJeffH: I see that this has been added to the WebAuthn Level 2 editor draft. Are there any plans on adding the attestation format the existing WebAuthn Level 1 spec as well, and if not, does this mean an implementation of the Level 1 spec should ignore the apple attestation format?

I also see that it hasn't been registered yet on IANA's page for attestation format identifiers. Would this have any implications for RP developers, or would it be fine to begin building support for this attestation format -- i.e. we could consider the IANA registration just a procedural step/formality?