从iPhone登录Twitter的困难

I'm using MGTwitterEngine to add Twitter functionality to my app. It's very easy to simply prompt the user for a username and password and then start posting. Strangely, however, I've noticed other apps (eg Foursquare and Brightkite) require you to visit their website to associate your Twitter account with your foursquare/brightkite/whatever account.I'm using MGTwitterEngine to add Twitter functi