SSH Agent support for WebAuthn keys

[carloscabanero]

OpenSSH does not support WebAuthn signatures inside the agent. We have explored a few possibilities with OpenSSH-dev mailing list https://lists.mindrot.org/pipermail/openssh-unix-dev/2022-September/040402.html.

I do see at least two interesting ways forward for this. One is to do this on OpenSSH, either through flags or any other method or idea we may come up with. The second is to release a Guardian Agent for Blink. This last one would be very interesting.

Please chime in if you have any other ideas.