IIS7 Basic Authentication on PHP Site

Question

I have a PHP5 site running on IIS7 and I just wanted to add basic authentication on a subfolder called admin.

I enabled both anonymous authentication and basic authentication and I just want to turn off anonymous authentication on the subfolder in order to force the basic authentication?

Any suggestions?

I tried adding a web.config in the subfolder with the following:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <system.webServer>
    <security>
      <authentication>
        <anonymousAuthentication enabled="false" />
      </authentication>
    </security>
  </system.webServer>
</configuration>