Create SSH Account from Website

I have one question, and still curious about it. How to create features on the website like this :

Creating SSH account from website.

Example: here

*There, you can create an SSH account by entering a username and password that you want at will. Unnecessarily complicated, simplify it.

So, I'm not going to put it on cPanel, but I will immediately apply it on a VPS. Why? Because according to the above features, the goal is to create an SSH account directly from VPS through the Website.

I wish there were pleased to share their knowledge here for my curiosity

Thank you :)