Shared SSO between two wordpress installs


I have two wordpress installs (one multisite, one Single install) and i would like the users to login with any creadentials (theirs of the first site, or theirs of the second site) independantly.
Does you WP plugin allow this ? I installed it on both sites, and setup 2 clients in the dashboard. But how to make this work please ?

Thank you

Also: two sites have different domain names