jp_one I'm trying to utilize SSL/TLS in order to securely communicate with flespi broker. Is my understanding correct, that luamqtt is not supporting certificate based authentication?
If you mean SSL/TLS secure transport for MQTT protocol - it's fully supported if your Lua runtime has a luasec (or compatible) module. And you can specify any custom SSL parameters like certificate file in the secure={...} table parameter in mqtt client instance constructor (see secure parameter description there).
If you are talking about new MQTT 5.0 packet type AUTH - it's also supported in the luamqtt with client:auth() method. But this is a broker-specific authentication method, thus you cannot use it with flespi broker.
jp_one So if token is regarded as not secure enough and luamqtt is used as MQTT client
Sorry, I can't understand this part. Can you please rephrase it?
jp_one the only way would to go would be via port 8883 or 443?
I would say that you always should use port 8883 and SSL/TLS secure connection.
But port 443 is for websocket transport, which is not supported by luamqtt.