From time to time you need to perform maintenance works on your systems; on such highly configurable systems like Communique these tasks can often be performed online while the authors are working. But some task require that there’s no activity on the system; when you want to reorganize your replication agents, it’s a very good feeling when nobody is trying to activate the super-duper important company news. So locking out the users is required.
A very easy method is available, when only superuser should have access. Because the superuser has no ACL, just add a “DENY all” ACL for all users. And the easiest way to do this is to add this ACL to the “post” user. Then the last ACL for every is a DENY to all handles. This effectivly forbids logins, forbids displaying any content for all users but the superuser.