Authenticator Attestation Response's [[transports]] should be an attribute rather than an internal slot. about webauthn

[emlun]

We would have done this if possible, but unfortunately this is not allowed by the Web IDL definition of an interface attribute:

An attribute is an interface member or namespace member [...]
[...]
The type of the attribute, after resolving typedefs, must not be a nullable or non-nullable version of any of the following types:

• a sequence type
  [...]

[[transports]] is of sequence type, so it cannot be an attribute of interface AuthenticatorAttestationResponse.

[emlun]

By the way, this is the same reason as for why getClientExtensionResults(), and a few others like it, must also be a getter method rather than a direct attribute.

[nbrr]

Thank you for explaining that @emlun. With this understanding and upon closer look, I notice that level 3 spec introduces use of toJSON(): this actually seems to address the frictions I mentioned?

[emlun]

Ah right - yes, it does! dictionary doesn't have this limitation, so the toJSON() outputs indeed include these getter results as plain attributes.