关于支持the Notification Service Extension

我们需要使用UNNotificationServiceExtension通知扩展服务，来对iOS端的远程推送消息进行修改。

其中要求

The system executes your notification service app extension only when a remote notification’s payload contains the following information:

• The payload must include the mutable-content key with a value of 1.
• The payload must include an alert dictionary with title, subtitle, or body information.

即Specifying the remote notification payload

{
	"aps": {
		"category": "SECRET",
		"mutable-content": 1,
		"alert": {
			"title": "Secret Message!",
			"body": "(Encrypted)"
		},
	},
	"ENCRYPTED_DATA": "Salted__·öîQÊ$UDì_¶Ù∞èΩ^¬%gq∞NÿÒQùw"
}

请问怎么设置上这个参数，使得aps中包含mutable-content