[webauthn] No way to select an intended authenticator during authentication with attachment info

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

== No way to select an intended authenticator during authentication with attachment info ==
[Section 4.4.4](https://w3c.github.io/webauthn/#attachment) describes the way for RP to set acceptable types of authenticators for registration and authentication. 
In case of registration, there is a member for this in MakePublicKeyCredentialOptions dictionary.
But, there is no such member for authentication option defined in PublicKeyCredentialRequestOptions dictionary.
IMO, PublicKeyCredentialRequestOptions dictionary must have authenticatorSelection member to provide for RP to select platform or roaming authenticator for authentication.


Please view or discuss this issue at https://github.com/w3c/webauthn/issues/583 using your GitHub account