For iOS : Hello, after reviewing the things and researching I derived that to get mutual friends, we need to call context.fields(mutual_friends).
So confusion is do I need to submit app to facebook for review? If yes, then which permission to select as I can see only "All Mutual Friends API" permission and it is clearly mentioned that all mutual friends api permission cannot be used at client side i.e in iPhone app.
My purpose is not to get all mutual friends, but only those use the app, so it will be suitable to select "All mutual friends"?
So do we need permission to get mutual friends(in addition to that both users have granted user_friends permission, and if yes, then what should be selected among permissions while submitting app for review to facebook?
Finally I got answer by developing and testing the process myself.
We don't need any extra permissions for getting mutual friends(apart from that both users, I and my friend have granted user_friends permission) who have used our app.