I have an iOS app where the users can login with Facebook and grant the user_friends permission. As of Graph API 2.0, Facebook claims you can't get all of the mutual friends between two people, you can only get the mutual friends that have also done Facebook integration in the app. However, apps like http://highlig.ht/ still seem to be able to do this.
What are some workarounds? Could I use an earlier version of the API somehow?
There is only one workaround for this: Use an App that was created before end of April 2014. That is the only way to use v1.0, but keep in mind that it will definitely stop working after April 2015.