Server required for auto-renewable subscriptions on iOS

Can someone explain to me what is required for Auto-Renewable subscriptions on iOS?

I'm confused as to whether it requires a server-side component (built by myself)? Or can everything be handled within the app?

Actually, this issue is fully covered in apple docs even with pictures and schemas

https://developer.apple.com/library/ios/documentation/NetworkingInternet/Conceptual/StoreKitGuide/Chapters/Subscriptions.html

Briefly:

1) You will need server-side if you want to make your subscriptions more flexible (ex: to add more sub-ns while app is in appstore) In this case your app gets list of subscriptions from server

2) You will be able to check the correctness of a transaction using your server by sending the received receipt to Apple-server, and give users the content if only the receipt is valid.