Sharing Cookies between Sub-domains

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If you have two sites using the same domain and would like to share cookies between them, set something like this in your settings.php file for each domain:

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

Be sure you include the leading '.' before the domain name or it won't work.

This allows users to maintain login status between any sites configured for domain-wide cookies.

This can also have negative side effects, so don't do this unless you're familiar with all the cookies involved for the sites you want to share cookies between.