Android, iOS and Windows WebView Apps

Hi Freelancers, I own a license to a PHP script that does not have a mobile app and I would like to create a very basic (WebView) based mobile app for Android, iOS and Windows Phone. My goal is to allow my users to log-in and 'stay logged-in' via native mobile functions and the rest can be webview. The entire site/script is responsive so it should look fine. I simply need them to be able to log-in and remain logged in (like how facebook and almost all other mobile apps do it) but in reality it's not a native app; it's just synced-up with my DB etc Please assist. Thank you