服务端验证自动续期订阅的收据过程如下：
服务端收到客户端发送的收据后，向苹果服务器发送post请求
苹果测试环境 https://sandbox.itunes.apple.com/verifyReceipt，
苹果生产环境 https://buy.itunes.apple.com/verifyReceipt
请求的http body是json格式，receipt-data字段对应的就是收据数据，password字段对应苹果开发账号设置的秘钥,exclude-old-transactions字段为true时，可过滤掉大部分旧的购买，只显示新的订阅。例如：
{
"exclude-old-transactions":true,
"password": "***",
"receipt-data":"***"
}
苹果服务器返回的http body里的status字段对应的是收据状态，若为0，则收据为真。
在receipt字段里，bundle_id 是APP的固定ID，可用于检查收据是否属于我们的APP。
在latest_receipt_info数组里，遍历数据，找到最大的expires_date，这个是订阅过期的日期，也可用expires_date_ms或expires_date_pst字段。服务器应保存该字段到数据库
product_id 是商品id，要与购买的商品ID相符才有效。
web_order_line_item_id 是本次购买的ID
original_transaction_id 是第一次订阅的交易ID，服务器应保存该字段到数据库
例如
{
"status": 0,
"environment": "Sandbox",
"receipt": {
"receipt_type": "ProductionSandbox",
"adam_id": 0,
"app_item_id": 0,
"bundle_id": "***",
"application_version": "6",
"download_id": 0,
"version_external_identifier": 0,
"receipt_creation_date": "2019-11-28 05:38:19 Etc/GMT",
"receipt_creation_date_ms": "1574919499000",
"receipt_creation_date_pst": "2019-11-27 21:38:19 America/Los_Angeles",
"request_date": "2019-11-28 08:18:12 Etc/GMT",
"request_date_ms": "1574929092579",
"request_date_pst": "2019-11-28 00:18:12 America/Los_Angeles",
"original_purchase_date": "2013-08-01 07:00:00 Etc/GMT",
"original_purchase_date_ms": "1375340400000",
"original_purchase_date_pst": "2013-08-01 00:00:00 America/Los_Angeles",
"original_application_version": "1.0",
"in_app": [
...
{
"quantity": "1",
"product_id": "***",
"transaction_id": "1000000598465716",
"original_transaction_id": "1000000598465716",
"purchase_date": "2019-11-28 05:38:19 Etc/GMT",
"purchase_date_ms": "1574919499000",
"purchase_date_pst": "2019-11-27 21:38:19 America/Los_Angeles",
"original_purchase_date": "2019-11-28 05:38:19 Etc/GMT",
"original_purchase_date_ms": "1574919499000",
"original_purchase_date_pst": "2019-11-27 21:38:19 America/Los_Angeles",
"expires_date": "2019-11-28 05:43:19 Etc/GMT",
"expires_date_ms": "1574919799000",
"expires_date_pst": "2019-11-27 21:43:19 America/Los_Angeles",
"web_order_line_item_id": "1000000048591202",
"is_trial_period": "false",
"is_in_intro_offer_period": "false"
}
]
},
"latest_receipt_info": [
{
"quantity": "1",
"product_id": "***",
"transaction_id": "1000000594693615",
"original_transaction_id": "1000000594693615",
"purchase_date": "2019-11-20 06:33:11 Etc/GMT",
"purchase_date_ms": "1574231591000",
"purchase_date_pst": "2019-11-19 22:33:11 America/Los_Angeles",
"original_purchase_date": "2019-11-20 06:33:11 Etc/GMT",
"original_purchase_date_ms": "1574231591000",
"original_purchase_date_pst": "2019-11-19 22:33:11 America/Los_Angeles",
"is_trial_period": "false"
},
{
"quantity": "1",
"product_id": "***",
"transaction_id": "1000000598475362",
"original_transaction_id": "1000000598465716",
"purchase_date": "2019-11-28 06:03:19 Etc/GMT",
"purchase_date_ms": "1574920999000",
"purchase_date_pst": "2019-11-27 22:03:19 America/Los_Angeles",
"original_purchase_date": "2019-11-28 05:38:19 Etc/GMT",
"original_purchase_date_ms": "1574919499000",
"original_purchase_date_pst": "2019-11-27 21:38:19 America/Los_Angeles",
"is_trial_period": "false",
"expires_date": "2019-11-28 06:08:19 Etc/GMT",
"expires_date_ms": "1574921299000",
"expires_date_pst": "2019-11-27 22:08:19 America/Los_Angeles",
"web_order_line_item_id": "1000000048591627",
"is_in_intro_offer_period": "false",
"subscription_group_identifier": "20577287"
}
],
"latest_receipt": "***",
"pending_renewal_info": [
{
"auto_renew_product_id": "jfldsjf",
"original_transaction_id": "1000000598465716",
"product_id": "jfldsjf",
"auto_renew_status": "0",
"expiration_intent": "1",
"is_in_billing_retry_period": "0"
}
]
}
收据应该保存在服务器里，当订阅到期时，再次用收据向苹果发送请求，更新用户的订阅到期时间。
在latest_receipt_info数组里，用original_transaction_id找到对应的交易，查看expires_date。若expires_date是过去的日期，表示用户没有续订。若expires_date是未来的日期，表示用户已续订。更新用户的过期日期。
latest_receipt是最新的收据，应保存到服务器数据库里，替换旧收据。
pending_renewal_info里的auto_renew_status表示是否还可能有后续的订阅，若为0表示用户已取消订阅
is_in_billing_retry_period为1表示用户支付信息有问题，苹果正在尝试重新扣款（最长持续60天），为0表示苹果停止重新扣款。
对于用户退款、更改订阅的行为的检查，服务器可与苹果建立服务端的连接，获取用户的订阅状态变化通知。开发账户中要设置服务器的URL。
