If I understand your question correctly, you can simply have the main script redirect the parameter to other scripts depending on its value.

#!/usr/bin/perl -wT

use strict;
use CGI;

my $q = new CGI;

my $class = $q->param("class");

my %scripts = ( prog1 => "prog1.pl",
                prog2 => "prog2.pl",
                prog3 => "prog3.pl",
              );

if ( $scripts{$class} ) {
    print $q->redirect("$scripts{$class}?class=$class");
} else {
    error("You don't have permission to access $class");
}

sub error {
    my $error = shift;
    print $q->header("text/html"),
          $q->start_html("Error"),
          $q->h1("Error"),
          $q->p("$error"),
          $q->end_html;
    exit;
}
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