Re: [webauthn] Update Virtual Authenticator API to better emulate synced passkey behavior (#2382)

After a good conversation with @kreichgauer today, I've simplified this PR somewhat by decoupling the signature counter from a virtual authenticator's default backup eligibility. Instead, both the **Add Credential** and **Set Credential Properties** endpoints have had `signCount` properties updated/added to normatively require that a credential's signature counter "MUST NOT increment" when `signCount` is set to `0`.

This slightly different direction should allow for RPs to write tests for authenticators that always return `0` for sign count, whether the authenticator can backup credentials or not. This should still solve my original problem over in #2363 that the signature counter always increments in getAssertion responses, which is not true for most modern platform authenticators and the macOS Chrome profile authenticator.

@emlun @pascoej @nsatragno @sbweeden @ve7jtb I think this is significant enough a change that I have to ask you all to re-review for approval 🙇‍♂️

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Received on Friday, 27 February 2026 20:25:05 UTC