title: How to implement facebook cross-apps authorization for iOS
body: <p>I'm developing mobile app for iOS 8 with Firemonkey (just for info) and my app works with Facebook. I did Facebook authorization though browser by specifying email and password. Everything works fine, but now I'd like to auto login to my custom iOS app without specifying email and password, if I <strong>already logged in</strong> to the <strong>native</strong> Facebook app. </p>
  
  <p>For example, we have two iOS 8 apps: 1) <strong>native</strong> Facebook app and 2) my <strong>custom</strong> app. All apps are logged out of Facebook. I login to native Facebook app, then open my custom app. How can my custom app retrieve access token from native Facebook app for auto login?</p>
  
  <p>I will be grateful for any code example in any programming language.</p>