my $q = CGI->new;
check_https($q);

sub check_https {
  my ($cgi) = @_;
  unless ($cgi->https) {
     my $url = $cgi->url(-path_info=>1, -query =>1);
     s/^http:/https:/ or die "Unsupported URI scheme, or https detection error";
     print $cgi->redirect($url);
     exit;
  }
}