Question

I was going through Facebook’s authentication mechanism.
and understood the client side, server side and desktop app processes.

But I couldn’t understand the iOS tutorial.
https://developers.facebook.com/docs/mobile/ios/build/

Where it talks about How Facebook SDK for iOS gracefully falls back to diff ways of authentication depending upon whats installed on users phone.

From the tutorial I understood that,

1. The API checks if facebook app is installed or not and if its
   there..it opens it and entire login process n pemission giving is
   done there and then the app redirects back to our app passing the
   authorization token, expiration, and any other parameters the
   Facebook OAuth server may return.

2. If FB app is not installed, Safari is opened and process happens
   there and access token is taken out of its cookies once it redirects
   back to the app.

3. And if iOS doesnt support multitasking, we cant open safari or any
   other app along with it,then it opens a UIWebView and carry on and
   access the token from its urlbar’s fragment area after #.

I got the third way which is what we do with a desktop app in .NET or air.

Can anyone explain the first n second ways ?

How can one app redirect the control to the other and how it can pass data to it.
and regarding the second way, how can the app read Safari’s cookies ?

Answer 1

It does it by opening a URL using UIApplication – openURL: and that URL will check if the facebook app is installed by using their custom URL ( http://iosdevelopertips.com/cocoa/launching-your-own-application-via-a-custom-url-scheme.html ). When that happens facebook then redirects back to your app using the same mechanism.

Read the documentation under //// private here: https://github.com/facebook/facebook-ios-sdk/blob/master/src/Facebook.m