There are two different things needed to setup the certificate authentification.
user certificates: There are N user certifiactes, one for each public key provided for signing.
helloworld-1234567890-1-cert.pub helloworld-1234567890-2-cert.pub ... helloworld-1234567890-N-cert.pub |
host certificate public key: There is one public key to authenticate servers.
yubikeyX.pub |