Question

I was wondering if it is possible to retain session information between a primary domain and a subdomain. For example, I login on http://www.mydomain.com/ but I want to use the same session on http://something.mydomain.com/.

Answer 1

Use session_set_cookie_params()

session_set_cookie_params ( $lifetime , '/', '.yourdomain.com');

Note, that the domain starts with a dot. This means, the session cookie is valid for every subdomain!

http://php.net/manual/en/function.session-set-cookie-params.php