iOS: ShareKit >> Twitter Settings >> Callback URL --- What is it?

I'm trying to implement ShareKit in my app; in the SHKConfig.h file, in the section where the Twitter applications settings are required, there is a line where I'm supposed to set the Callback URL:

I have opened a Twitter application on Twitter and filled all the fields there, but I'm not clear regarding to what data should be inserted in the Callback URL field:

Can anyone explain?

The callback parameter you write in your application settings in Twitter is ignored, you can write anything, example: http://www.google.com (anything will do since it is ignored).

When you add a callback url in the #define, its value will be sent to twitter in the owner authorization step, and will override the value that you previously wrote in the Twitter website. Weird, I know. It's related to this security vulnerability.

The callback parameter is the URL Twitter is going to send the user after authentication. When running in websites instead applications, the URL callback is used to recover control of the OAuth flow.

On Applications, you can set it to a custom scheme like myapplication://twitter and then register the scheme myapplication in your app. This way, after authentication, the Twitter website running in UIWebView or Safari launches that URL, which iOS knows is assigned to your app, and that's how you recover control of the OAuth flow.

That's the theory, I don't know exactly how ShareKit works. It may be that it runs the authentication on a UIWebView and detects the activity of the user to recover control manually, which is another way to do it.