Is it possible to set a cookie for http://www.example.com from a PHP file located at https://secure.example.com? I have some code that was given to me, that appears to try and fails at this. I was wondering if this is possible at all.
Webpages can only set cookies for the second (or higher) level domain that they belong to.
This means that secure.example.com can read and set cookies for secure.example.com or .example.com, the latter of which can also be read and set by www.example.com
One last note: If the secure flag is set on a cookie, it can only be read and set over an https connection.
If you set the cookie domain to ".example.com", the cookie will work for all subdomains.
来源：https://stackoverflow.com/questions/2465036/setting-cookies-for-multiple-sub-domains