How does libfido2 handle incrementation of assertion signature counters?

[apantina]

In the webauthn spec it is described how assertion signatures contain a counter that gets incremented upon a successful assertion. Does libfido2 handle this? I dug around the codebase a bit and I couldn't find any logic that would handle this.

I found fido_assert_sigcount https://developers.yubico.com/libfido2/Manuals/fido_assert_sigcount.html but it seems like the underlying variable isn't getting incremented anywhere in the libfido2 code (correct me if I'm wrong, of course).

The reason that I ask this is that I am implementing some logic that involves getting a challenge from an authentication backend, interacts with the Yubikey via libfido2 by using fido2-assert -G and finally sends the signed assertion back to the backend for verification. The issue is that on subsequent calls of fido2-assert to the same authenticator (and the same pubkey handle) the counter doesn't get incremented. As a result of this I'm unable to get a successful response from the backend as it expects that the counter is incremented from the previous call as the spec dictates.

Hope this question makes sense, thanks in advance!

[apantina]

Marking as resolved, the counter does seem to get incremented, there was an issue with how the authenticator data was being parsed.