How would I interconnect a server with a game launcher in Java?

How would I interconnect a server with a game launcher in Java?

I'm currently working on a game in Java. I will be creating a launcher
with the game itself and wrapping it with some .exe wrapper. What I need
help with is getting the game to connect to some sort of server and check
if the credentials for the user are true:
Username is REAL.
Password matches that listed with username.
User has bought game (true/false) AKA is user premium?
It has to work with a website that uses PHP and HTML. When the user
creates an account, it is stored both in the website, and in the game
server itself. Also, if there's an update for the game, it automatically
updates itself by getting the files from the server.
The concept is rather similiar to games like Minecraft and Planetside 2.