Thank you very much for your answer.
Since the question was about coding, I should I have used the other forum, the one that has no "coding" in the title :-)
BungeeCord seems like a reverse proxy to create a hub, so what I was looking for is Spigot. I'd like to take a look at SCB code and I found a version for Spigot, though I'm afraid CCG most likely use a custom private version.