SSH into the NexOSS box
Become the root user
Execute the following command replacing USERNAME with the username you want to add (you will be prompted for a password):
htpasswd /etc/munin/munin-htpasswd USERNAME
SSH into the NexOSS box
Become the root user
Execute the following command replacing USERNAME with the username you want to change the password for (you will be prompted for a password):
htpasswd -c /etc/munin/munin-htpasswd USERNAME