PHP Cloudfront SetCookie

http://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/private-content-setting-signed-cookie-custom-policy.html

他们给出了一个示例cookie标题：

Set-Cookie: Domain=d222221abcdef8.cloudfront.net; Path=/; Secure; HttpOnly; CloudFront-Key-Pair-Id=APKA9ONS7QCOWEXAMPLE

我创建了以下PHP代码

setcookie (
  'CloudFront-Key-Pair Id','MYID','/','mycloudfrontsub.cloudfront.net',true,true
);

但是没有设置cookie.只有在我取出域名时才设置cookie.

我认为这是因为在session_start之后在脚本中调用了setcookie.我尝试添加这个,但是在session_start()之前需要它

session_set_cookie_params(0,'duvoxso6rm38g.cloudfront.net);

我需要做这样的事情吗？

//close local session,then open new one for aws
$id=SID;
session_write_close();
session_set_cookie_params(0,'mysub.cloudfront.net');
session_start();
setcookie(...);
session_write_close();
session_set_cookie_params(0,'originaldomain.com');    
session_start();