I in fact have done this (heavy user of smart cards and author of middleware), BUT what sshd logs (a fingerprint of the public key) requires a bit of work to ma

I in fact have done this (heavy user of smart cards and author of middleware), BUT what sshd logs (a fingerprint of the public key) requires a bit of work to match an authorized_keys format file (basically a stripped down PKCS#1 format with a header). I actually use a fork of OpenSSH called PKIXSSH which supports X.509 certificates in sshd, and this is far more reliable.