I do not want our wiki to be visible to the public. Only registered users should be able to view the wiki.
There only seem to be options to block specific users or IP addresses. I want to block all except registered users.
How do I do that?
Specifically the 'Simple Private Wiki' information;
Simple private wiki
For the common use case of "a private wiki, for oneself and approved others", you need to:
Restrict account creation
Hope this helps.