I've edited the file /opt/alfresco/tomcat/shared/classes/alfresco/extension/ldap-authentication-context.xml.sample and renamed in ldap-authentication-context.xml (in the same directory).
Now I can login with LDAP users, but I still aven't setup a specific repository with "group" authorization (only members of a specific group can access the repository).
If someone has done this task, please reply..
PS I'm looking for CIFS authentication through OpenLDAP.