Group containing all users, dilemma

Hello again, I need in my wiki this configuration xwiki level: everything is restricted to admins namespace X: everyone (connected or not) has read access. Problem: If i put nothing at namespace X level, nobody except admins can read documents If i define read access at namespace X level, i need to know what i have to put in user/group to define 'anyone' You could of course tell me to use a combo of guest and XWiki.XWikiAllGroup, but unfortunately, our user are not created using the registration interface. They are mapped to an ldap server. So the XWiki.XWikiAllGroup stays empty. Unless, of course, this is a virtual group which says always true when asked if xyz belong to it. But it doubt it's virtual :) So, what are suggestions about this? regards, Tchize