Each request passes through several stages in the web server. Authentication and authorisation happen before the CGI script is run and, in fact, the web server does not pass the password to the CGI program at all (that could lead to security problems).

You'll need to add mod_perl handlers for this. Look at The mod_perl Guide for more info.

You can do it with FastCGI too, I believe. I think FastCGI supports authentication as well as normal request handling. Information on that would probably come from the fastcgi.com web site.