[webauthn] txAuthSimple does not conform to extension requirements

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

== txAuthSimple does not conform to extension requirements ==
As per https://w3c.github.io/webauthn/#sctn-simple-txauth-extension, the authenticator extension input is a CBOR string.  

As per https://w3c.github.io/webauthn/#sctn-authenticator-extension-processing, the authenticator extension input is a CBOR map.

Suggested change:  proponents of this extension define the authenticator extension input as a CBOR map.  I will modify https://github.com/w3c/webauthn/pull/724 accordingly when this is done.

Please view or discuss this issue at https://github.com/w3c/webauthn/issues/725 using your GitHub account