i Have setup 2 domains/sites in the ISPConfig on amazon Web server EC2 instance,
i have a domain named app.example.com and the other is https://www.example.com Both dom
The first comment of @Alan Gularte replies quite well I think. If it does not work, you may consider writing a cookie yourself to pass info back and forth.
setcookie ("PassMySessionName", $_SESSION['user_name'], time() - 3600, "/", "example.com");
Setting cookie domain to "example.com" will make it available both on www. and app.
On the other side you will find it in the $_COOKIE array.
$PassedUserName=$_COOKIE["PassMySessionName"];
If you need it all to work without cookies enabled, it gets much more complicated, as $_SESSION will work appending parameters to your urls transparently. In that case (if you link from one site to the other) you may add them manually to the urls.
I would like to make a little correction,
Bad: setcookie ("PassMySessionName", $_SESSION['user_name'], time() - 3600, "/", "example.com");
Correct: setcookie ("PassMySessionName", $_SESSION['user_name'], time() + 3600, "/", "example.com");