[webauthn] §9.2 requires client extension output but appidExclude sets none (#1445)

emlun has just created a new issue for https://github.com/w3c/webauthn:

== §9.2 requires client extension output but appidExclude sets none ==
[§9.2. Defining Extensions](https://w3c.github.io/webauthn/#sctn-extension-specification) reads:

>Any client extension that is processed by the client MUST return a client extension output value so that the WebAuthn Relying Party knows that the extension was honored by the client.

[§10.2. FIDO AppID Exclusion Extension (appidExclude)](https://w3c.github.io/webauthn/#sctn-appid-exclude-extension) reads:

>*Client extension output*
>None.

At least one of these should change, as the spec is internally inconsistent as is.

Please view or discuss this issue at https://github.com/w3c/webauthn/issues/1445 using your GitHub account