username             (string)    MQTT username
password             (string)    MQTT password
qos                  (number)    set the quality of service priority, defaults to '0'
keep_alive_interval  (duration)  keep-alive interval for MQTT connections in s,m,h,d
reconnect_interval   (duration)  reconnect interval for MQTT connections in s,m,h,d
queue_dir            (path)      staging dir for undelivered messages e.g. '/home/events'