[xwiki-users] xwiki spaces access rights

Hi, I just installed xwiki. Reading about access rights I got the impression that I could use spaces, to determine which user can access a group of pages. I wanted to have a wiki, so I could work in collaboration with my clients on some documents. Since client A cannot be allowed to access client B information, I thought spaces would solve that problem. So I created two spaces. ClientA and ClientB spaces. I also created two groups called clientA and clientB. And two users user1 and user2. User1 is part of group clientA and user2 is part of group clientB. In each space administration page only one of the groups has all the boxes checked. All the other boxes are unchecked. But if I log with user1 that belongs to clientA I can view and edit pages of clientB space. How can I restrict things so that user1 can only view/edit/delete on pages that are on space clientA?