I have website 1 (www.website.com)
and website 2 (www.website.com/private

I am using a plugin to set up single sign on between my other php site and WordPress.

This works fine on a subdomain (www.website.com & private.website.com with define(‘COOKIE_DOMAIN’, ‘website.com’);

On the subdirectory set up
define(‘COOKIE_DOMAIN’, ‘website.com’);
This will make the login loop forever and never login.

define(‘COOKIE_DOMAIN’, ‘website.com’);
define(‘COOKIEPATH’, ‘/private’);
This will work for a short while but then cookies on website 1 (www.website.com) will stop working and you cannot login and the pages will not load anything.