Include the "Easily accessing credential data" fields in JSON.

[agl]

The WebAuthn API provides accessors to get the SPKI-formatted public key and authenticator data without needing to parse CBOR or handle COSE. However, the JSON structures, prior to this change, didn't include these values giving users an unfortunate choice: either use the accessors and do the JSON encoding yourself, or use the provided toJSON function.

But we can have both!

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Preview | Diff

[MasterKale]

lgmt lgtm

[emlun]

LGTM, with or without the below suggestion.

[agl]

(from the call of 2023-05-17: good to merge when checks are happy.)

[emlun]

I realize belatedly that we probably also need instructions on how to populate these new fields, like we have for clientExtensionResults and transports:

webauthn/index.bs

Lines 1592 to 1602 in 6dfbdba

	The
	{{RegistrationResponseJSON/clientExtensionResults|RegistrationResponseJSON.clientExtensionResults}} or
	{{AuthenticationResponseJSON/clientExtensionResults|AuthenticationResponseJSON.clientExtensionResults}}
	member MUST be set to the output of {{PublicKeyCredential/getClientExtensionResults()}},
	with any {{ArrayBuffer}} values encoded to {{DOMString}} values using
	[=base64url encoding=]. This MAY include {{ArrayBuffer}} values from extensions registered
	in the IANA "WebAuthn Extension Identifiers" registry [[!IANA-WebAuthn-Registries]] but not
	defined in [[#sctn-extensions]].
	The {{AuthenticatorAttestationResponseJSON/transports|AuthenticatorAttestationResponseJSON.transports}}
	member MUST be set to the output of {{AuthenticatorAttestationResponse/getTransports()}}.

I'll open a follow-up PR.

[emlun]

I'll fix the above issue in PR #1906.