1. apple in-app purchases

1.iap in-app payment process
	1. The user enters the purchase virtual item page, the App obtains the product list from the backend server and displays it to the user
	2. The user clicks to buy to buy a certain virtual item, (you can send it to the server to generate an order first, after success) the APP sends the productionIdentifier of the virtual item to the Apple server
	3. The Apple server returns the corresponding item information (description, price, etc.) according to the productionIdentifier sent by the APP
	4. The user clicks the confirm button to purchase the item, and the purchase request is sent to the Apple server
	5. After the Apple server completes the purchase, it returns the user a voucher for completing the purchase
	6. The APP sends this credential to the background server for verification
	7. The backend server sends the credential to Apple for verification, and Apple returns a field to the backend server to indicate whether the credential is valid
	8. The background server sends the verification result to the APP, and the APP performs corresponding processing according to the verification result

Notice:
	1. Man-in-the-middle attack
	2. Determine the return code of Apple's official verification server. If it is 21007, then connect to the test server again for verification.
	3. Client upload credentials should be persistent

https://developer.apple.com/cn/in-app-purchase/

https://www.jianshu.com/p/a4e6c4ef6de4
https://developer.apple.com/cn/
https://blog.csdn.net/jjjjjj123321/article/details/78481248
http://blog.devtang.com/2012/12/09/in-app-purchase-check-list/
http://blog.devtang.com/2013/04/07/tricks-in-iap/
http://www.iwangke.me/2013/02/18/get-itunes-raw-response-with-mitmproxy/
https://blog.csdn.net/u012960049/article/details/51899157