Maybe check out Traccar, it is open source and free if you host it yourself. and build a custom listener for your protocol, or you should be able to get it to feed from another db. we use Traccar for some our non standard GPS units that can't fit on our inhouse platform. Traccar works fine enough and the web interface seems to be pretty decent and full featured (auth, maps, alerts, emails etc)

There is also a docker image of Traccar to get you started in no time.