vi /etc/ssh/sshd_config

PermitRootLogin prohibit-password

PasswordAuthentication no
RSAAuthentication yes
PubkeyAuthentication yes

Match User alice,bob,john
PasswordAuthentication no

DenyUsers johnd admin nagios

DenyGroups wheel adm video apache

Deny Users johnd admin nagios

Address Family inet

 systemctl restart sshd

• https://tecadmin.net/deny-allow-access-for-users-and-groups-in-openssh/
• https://www.xmodulo.com/how-to-force-ssh-login-via-public-key-authentication.html
• https://blog.stephane-robert.info/docs/securiser/durcissement/ssh/