Raneto is secure because it doesn't have any kind of interface that can be hacked (e.g. a login page). To make changes to Raneto content you need to have access to your server file system.
i think the question was asking for most of the content publicly accessible but some of the content hidden behind a login. google sites does something like that but i haven't seen any flat-file cms'es that offer it.
I believe he's not talking about authentication, he's talking about access/authorization.