Re: [webauthn] feature policy integration (#1214)

WRT integrating [Feature Policy (FP)](https://www.w3.org/TR/feature-policy/) with  [`isUserVerifyingPlatformAuthenticatorAvailable()`](http://w3c.github.io/webauthn/#isUserVerifyingPlatformAuthenticatorAvailable): the latter's impl is [client-platform](http://w3c.github.io/webauthn/#client-platform)-specific.

I _suppose_ we would want it to [return an error](https://www.w3.org/2001/tag/doc/promises-guide#errors) if webauthn is "Disabled" in the calling context?

If so, would this build on the present text in the [iUVPAA() section](http://w3c.github.io/webauthn/#isUserVerifyingPlatformAuthenticatorAvailable) work?  One issue is that [iUVPAA()](http://w3c.github.io/webauthn/#isUserVerifyingPlatformAuthenticatorAvailable) returns a boolean -- can that also be morphed into an error code?  [Promises are only sposed to _return_ errors, not throw them](https://www.w3.org/2001/tag/doc/promises-guide#always-return-promises). First parag is unchanged, only added the Note:

> WebAuthn Relying Parties use this method to determine whether they can create a new credential using a user-verifying platform authenticator. Upon invocation, the client employs a client platform-specific procedure to discover available user-verifying platform authenticators. If any are discovered, the promise is resolved with the value of true. Otherwise, the promise is resolved with the value of false. Based on the result, the Relying Party can take further actions to guide the user to create a credential.
>
> Note: Invoking this method from a [=browsing context=] where the [=Web Authentication API=] is "disabled" according to the [=allowed to use=] algorithm—i.e., by a [=feature policy=]—will result in the return of an error code equivalent to "{{NotAllowedError}}".
>
> This method has no arguments and returns a Boolean value.



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Received on Thursday, 9 May 2019 18:25:20 UTC