Hello I personally use php periods (not snacks, aside from session id cookie) for those user data, so when a person would go to their profile user.mydomain.com they're immediately "drenched out" untill then take away the subdomain.
It is possible to method to accept periods all domain names as lengthy since it's *.mydomain.com
Listed here are 3 options.
Place this inside your php.ini:
session.cookie_domain = ".example.com"
Inside your .htaccess:
php_value session.cookie_domain .example.com
Because the first factor inside your script:
ini_set('session.cookie_domain', '.example.com' )
Make sure to check this out thread too, as it is related: