Private web app

I have created an android app for my workplace using phonegap.

It contains sensitive information, so it’s password protected, and installed via sideloading to keep it off the play store.

But it’s tiresome to get everyone to reinstall it every time there’s an update.

What I want to do, is for the app to be a shell, and the information retrieved from the web.

How do I set up the site so it will only respond to requests from the app?