如何在App购买自动更新订阅中进行检查?

I'm looking to implement the new Auto Renewable subscriptions using In App purchase but I am unsure how or when to check if the user is currently subscribed. My understanding is that when the user initially subscribes the app can use the purchase date along with the subscription date to calculate how long their subscription would last. What happens after this date has passed? How do we check if the user has auto renewed or cancelled?I'm looking to implement the new Auto Renewable