How to set cookie in one domain that is readable by another domain

Question

I have two domains that I want to communicate. I want the first domain to set a cookie in the second domain telling the second domain that the current user is known to the first domain. I understand that I cannot read cookies for another domain, but given that I have access to both, is there a way to accomplish this?

Both domains are implemented in PHP. One is a Drupal site and the other a WordPress site.

Answer 1

Server can't read cookie for another domain but, you can add cookie for another domain. When adding cookies, you should add double cookie. First your normal cookie and second for another domain. Both values are the same.