How do user management work - for services

In “MQTT Server & Web client” which I have trouble starting its possible to write a username/password in the config part of the plugin. Should i create a user for it in setttings>Users and if Yes, than how do i give a newly crreated user a password!?

My config of it, looks like this (i couldnt find the thing im supposed to insert around code (danish keyboard)):

“ssl”: false,
“certfile”: “fullchain.pem”,
“keyfile”: “privkey.pem”,
“broker”: true,
“allow_anonymous”: true,
“mqttusers”: [
“username”: “”,
“password”: “”,
“readonly”: true,
“topics”: [