WordPress multisite use same login cookie for both multisites pages.

WordPress multisite use same login cookie for both multisites pages.
I need that both pages on multisite network would have same login cookies, so if the same user is logged in on one site, and if it exist in other one – login him automatically !

It was like that on my solution, but dont know why now it is not like that, now you have to login separately on both pages even when the username password and etc is the same. It does not work since we have changed the server of the pages.

The sites have different domains.

How to do so ?