Forbid password login on DO's droplet

This link from digitalocean.com about how to use ssh key as login is very good. But the last part about shutting down login with password doesn't work on my droplet. If I only set the

PermitRootLogin without-password

other computer still gets prompt asking password.

So I modified PasswordAuthentication to

PasswordAuthentication no

Finally other computer doesn't prompt password input requirement.

If you only want to deny root login with password:

Match User root
    PasswordAuthentication no

Simple.