mosquitto_passwd -h
mosquitto_passwd is a tool for managing password files for mosquitto.
Usage: mosquitto_passwd [-c | -D] passwordfile username
mosquitto_passwd -b passwordfile username password
mosquitto_passwd -U passwordfile
-b : run in batch mode to allow passing passwords on the command line.
-c : create a new password file. This will overwrite existing files.
-D : delete the username rather than adding/updating its password.
-U : update a plain text password file to use hashed passwords.
See http://mosquitto.org/ for more information.