Password protect a folder in CI

Hi, i've kept application and system folders out of public_html to be safer.
As you guessed this is what i got:
-/public_html
--/img
--/css
--/js
--/dir-to-protect/file-to-protect.php
--index.php (CI's index)
--and of course .htaccess robots.txt sitemap.xml etc.. ( to let you know i'm a good boy

Thanks