Sometimes you want SSH rules to just apply to a single user or group. For example allowing password login from a single user account while forcing other users to use certificates. The sytax is simple, at the bottom of your /etc/ssh/sshd_config file put:

Match User user1
PasswordAuthentication yes

Where user is the username you want to target and

PasswordAuthentication no is the command you want to apply to that user. You can target groups with:

Match Group users

or invert the selection with !:

Match User !root

Source serverfault.com