xmlHttpRequest怎么设置cookie

Creator 2.x
#1 
post(url:string, date:{}, callbacks){
        let xhr = new XMLHttpRequest()
        xhr.open("POST", url, true)
        xhr.setRequestHeader('content-type', 'application/json')
        xhr.setRequestHeader('cookie', 'sessionid='+window["Sessionid"])
        xhr.onreadystatechange = callbacks(xhr)
        let sendData = date
        let sendDatao = JSON.stringify(sendData)
        xhr.send(sendDatao)
    }

assets\Script\root.ts:46 Refused to set unsafe header "cookie"
拒绝设置不安全的标头“cookie”

任何人都可以回到这个问题。