Connecting the login flow between Android/iPhone app and the web

When the person opens my app, I want to display a button. The user clicks this button, and it opens a browser (embedded, of course) inside the app, allowing the user to LOGIN through that web page.

Of course, when the person logs in, it only logs in to that web server. The web service now knows that the user is logged in.

As the user uses my mobile app开发者_运维问答, I need to know if he's logged in or not. How can I know? There's no way for my app to determine if the user is logged into my web service.

By the way, I am using Django framework for my web service.

Well, presumably when your user logs in the server is telling their browser to set a cookie. Why not just capture this cookie and use it to determine if they successfully logged in?