How to get all contacts/email ids with users permission from gmail , yahoo, Facebook , phone contacts?

Basically i want to implement feature in my iOS app where i get all emails from respective account and use these email-id(s) to check whether these users are using my app.

Invite friends button will show popup showing major accounts like google , Facebook and ask to enter credentials if required to get all ids.

This is an iOS feature. I am completely clueless about this implementation.