How to on Multisite manage users over 1 site My client need 13 Pages with different domains, so we decided to make different DBs with same codebase. Now, he want to manage the users (admin, editors) over 1 site, so he can select which user has access to which site. 

We tested CAS which works so far but i'm not able to define which user has access to which site.

How can I do that?
LDAP, you should define in an external directory (openldap, AD or whatever) which website a user can access or not and define rules inside each website (mapping rôles/sites/ldap properties, more infos here).
From there, you can add SSO like CAS.