In IIS 6, you could turn on Authentication by right clicking an application, selecting properties, going to the Directory Security Tab, selecting Edit in the Authentication and Access control group box, and setting Authenticated Access to "Basic Authentication (password is sent in clear text)"
In IIS 8.5, I don't see a similar option in the Authentication Menu:
Here's are the docs on Basic Authentication and it says you should just be able to enable it
http://technet.microsoft.com/en-us/library/hh831496.aspx#Basic
But I don't see it anywhere.
Turns out, if you can't see Basic Authentication as an option, you'll need to manually enable that feature in IIS.