Hello,
I'm using Zen Cart, Authorize.net, and PayPal. I've successfully restricted access to the directory containing the shopping cart. Unfortunately, doing so breaks the checkout functions. What I want to do is restrict access to this cart only to valid-users or requests coming from authorize.net or paypal. Here's my .htaccess:

Unfortunately, its not working. I've tried using

which does present the password prompt; but breaks checkout. I've looked all over Zen Cart's forum and various and sundry places and haven't been able to get a good answer.
I appreciate any help.

Is this on a shared server? If so you will need to contact technical support.

The only directives allowed in a .htaccess file by default are very restrictive in our shared environment.