DHCP MQTT Lease Publish on Asus Merlin router. Put the script wherever you want and put the dnsmasq.conf.add into /jffs/configs

dhcp_lease_mqtt_publish

#!/bin/sh

if [ "$#" -ne 4 ]; then
    echo "Illegal number of parameters"
    exit 1
fi

MQTT_CAFILE="/mnt/sda1/ssl/ca.crt"
MQTT_SERVER="<SERVER_HERE>"
MQTT_PORT="8883"
BASE_TOPIC="network/dhcp"
BIND_ADDR="192.168.250.1"
CLIENT_CERT="/mnt/sda1/ssl/client.crt"
CLIENT_KEY="/mnt/sda1/ssl/client.key"

MOSQUITTO="/opt/bin/mosquitto_pub"

op="${1:-op}"
mac="${2:-mac}"
ip="${3:-ip}"
hostname="${4}"

tstamp="`date '+%Y-%m-%d %H:%M:%S'`"

topic="${BASE_TOPIC}/${mac}"
payload="${op} ${ip} ${mac} ${tstamp} (${hostname})"

"${MOSQUITTO}" --quiet -A "${BIND_ADDR}" \
-h "${MQTT_SERVER}" -p ${MQTT_PORT} \
-t "${topic}" -m "${payload}" -r \
--cafile "${MQTT_CAFILE}" --cert "${CLIENT_CERT}" --key "${CLIENT_KEY}"

exit $?

dnsmasq.conf.add

dhcp-script=/mnt/sda1/helpers/dhcp_lease_mqtt_publish