For the list archive -- and maybe the faq, if any:
The setting to require login before users can edit pages in phpwiki 1.3.7 turns out to be in the file wiki/index.php. As mentioned elsewhere, the variable is REQUIRE_SIGNIN_BEFORE_EDIT and the default of 'false' must be changed to 'true.' The same setting exsists in the file config/config-dist.php, for what reason I don't know, but changing it there doesn't affect the wiki's behavior in any noticeable way.
Have fun, all.