Sharing SESSION Variables Between Multiple Subdomains

Question

I have a website www.example.com. That will have multiple subdomains that work with a single application or program. For an example, login.example.com will allow the user to log in to the site while system.example.com will allow the user to access an information system, while forums.example.com will allow the user to access forums.

We may need to pass information between the subdomains such as a user id, or a user preference, etc. How do we go about passing information between the sudomains using SESSION variables?

EDIT: I like this idea:

As the first thing in your script:

ini_set('session.cookie_domain', '.example.com' ); 

Answer 1

1) the subdomains should use the same path to save session files

2) modify your

php.ini session.cookie_domain = ".example.com"

or .htaccess php_value session.cookie_domain .example.com

or inside of the script ini_set('session.cookie_domain', '.example.com' );