PHP Sessions across subdomains

PHP sessions can be shared across subdomains by setting the session cookie's domain to the top-level domain. This can be done by calling the session_set_cookie_params() function and passing in the desired domain as the second parameter. For example, to share sessions across all subdomains of example.com, you would use: session_set_cookie_params(0, '.example.com'); It's important to note that the browser may not allow cookies to be shared across different subdomains if the subdomains are not under the same parent domain.