Share the method of php using P3P to complete COOKIE cross-domain operations

127.0.0.1 www.a.com
127.0.0.1 www.b.com

First: Create a_setcookie.php file:

//header('P3P: CP="CURa ADMa DEVa PSAo PSDo OUR BUS UNI PUR INT DEM STA PRE COM NAV OTC NOI DSP COR"');

setcookie("test ", $_GET['id'], time()+3600, "/", ".a.com");
?>

Then: Create a_getcookie.php file:

var_dump($_COOKIE);
?>

Finally: Create b_setcookie.php file:

Three After the files are created, access them sequentially through the browser:

http://www.b.com/b_setcookie.php
http://www.a.com/a_getcookie.php

while visiting the b.com domain, and There is no cookie value set in the a.com domain.

Then, modify the a_setcookie.php file and remove the comment symbols. a_setcookie.php is:

header('P3P: CP="CURa ADMa DEVa PSAo PSDo OUR BUS UNI PUR INT DEM STA PRE COM NAV OTC NOI DSP COR"');

setcookie("test", $_GET['id'], time()+3600, "/", ".a.com");
?>

Visit through the browser again:

http://www.b.com/b_setcookie.php
http://www.a.com/a_getcookie.php

to see if cross-domain has been implemented Visited.