"Opaque data" extension

Here is a first attempt.
-Giri

Authenticator Data (AuthData) Extension
Extension identifier
webauthn.authdata
Client argument
N/A
Client processing
N/A
Authenticator argument
N/A
Authenticator processing
This extension is added automatically by the authenticator. This extension can be added to attestation statements and signatures.
Authenticator data
The AuthData extension is a binary payload that is sent from the authenticator to the relying party.