arduino as ewlink

hello guys, I would like to understand how the communication between the sonoffs and the server and the app works.
I would like to create a communication system with my devices using an external bridge server so as not to open the doors on each device, just like the sonoffs, I currently use http requests. What do you recommend for communication?
I don't want to use mqtt or others to avoid libraries or compatibility, something simple, universal and safe, what do you recommend?