Where does OpenHAB Cloud store the users' data

Hey, I’ve been using OH2 for months and I want to dig in so that I can understand about the system more.
Since I found on github the directory of OpenHAB Cloud and follow the tutorial on this community about setting my own cloud, I succeeded in installing it and I’m really excited!

But I wonder where does OpenHAB Cloud store the registered user accounts?
And how it can authorize one account to be master account and the others are just “users”? I mean what are the steps to do that? Can a instance have more than just one master account?

I want to contribute to this community, but first I need to understand what the developers did ! Please help me!