Just tried the following lines in CLI:
uci set mosquitto.mqtt.remote_username=username here
uci set mosquitto.mqtt.remote_password=password here
uci commit mosquitto/etc/init.d/mosquitto restart (please check should be like this in one line?)
Outcomes: Still not working.
--- The username filed has been filed (but still showing a red boarder on the filling filed.)
--- The password filed is still filled with "test", not been updated.