Support certs / CA auth.

[YellowOnion]

It would be nice to support "User CA's".

https://man.openbsd.org/ssh-keygen#CERTIFICATES

There's already pam_ussh but it's more dependencies than integrating it with this project.

[programmerq]

I just tried this and found it didn't work. Adding the error message in case it helps someone find it:

Jun 01 15:28:34 brain sudo[1955519]: pam_ssh_agent_auth: error: key_from_blob: remaining bytes in key blob 1294
Jun 01 15:28:34 brain sudo[1955519]: pam_ssh_agent_auth: Failed Authentication: `jeff' as `jeff' using /home/jeff/.ssh/authorized_keys

My keys that are not certs work with my config.