I can write the same in PHP so that You get an authenticated GUI for user management.
Rest assured you will get the best of quality and security. Also, my solution will run from any machine be it Windows, Linux or Mac. All you need is a browser.
Actually, I can write in any language but I believe you want ease-of-use and simplicity to manage users in Linux System and hence proposed PHP for this. The solution is going to be platform independent and can be accessed anytime from anywhere using the browser, even from the phone.
I've been doing such kind of automation job for several of my clients. I hope I bag this project and get you an awesome solution that works out of the box without any hiccups.