[webauthn] Clarify the valid values for user handle in the Authentication Assertion (#1723)

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

== Clarify the valid values for user handle in the Authentication Assertion ==
The [5.4.3. User Account Parameters for Credential Generation](https://www.w3.org/TR/webauthn-2/#dictionary-user-credential-params) requires that the user handle must not be an empty string.
However, the [5.2.2. Web Authentication Assertion (interface AuthenticatorAssertionResponse)](https://w3c.github.io/webauthn/#iface-authenticatorassertionresponse) does not explicitly say if userHandle may be an empty string. I would infer that it must be either null, or the same value as passed under `PublicKeyCredentialUserEntity` when registering.

At the moment not all browsers have consistent behavior. For my authenticator (YubiKey) Firefox and Chromium always return `userHandle: null`. However, Safari returns `userHandle: ""`. I opened a [bug report](https://bugs.webkit.org/show_bug.cgi?id=239737) for Safari based on my understanding of the authentication part of the WebAuthn spec.

Please view or discuss this issue at https://github.com/w3c/webauthn/issues/1723 using your GitHub account


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Received on Monday, 25 April 2022 19:41:34 UTC