$form_data = join '&',
             map { my $key = $_;
                   my $val = $form_data{$_};
                   $key =~ s/([^A-Za-z0-9])/sprintf("%%%02X", ord($1))/seg;
                   $val =~ s/([^A-Za-z0-9])/sprintf("%%%02X", ord($1))/seg;
                   "$key=$val" }
             sort keys %form_data;