I've seen examples where it's easy via CGI.pm's header() function to add arbitrary fields to the response HTTP header, but is there an easy way to retrieve arbitrary fields from the request's header?

ok, so adding an arbitrary field to the response's header is easy:

print $query->header(-type=>'image/gif',
                        -status=>'402 Payment Required',
                        -expires=>'+3d',
                        -cookie=>$my_cookie,
                        -charset=>'UTF-7',
                        -attachment=>'foo.gif',
                        -Cost=>'$0.02');
[download]

"Cost: $0.02" would be added to the response's header. But if "Cost: $0.02" were part of the CGI request's header, how should I retrieve this?

This is my first question posted here, and many thanks in advance for any responses.