If I understand you correctly, then you're middleware is attempting to translate a set of key/value pairs from the user into a URL which is passed to your third party app.

I'll assume that the user input is pre-processed into a hash, and so you need to

1. Strip out keys that have no meaning to the app
2. Regularise the hash to ensure that the keys have the right case
3. Turn it into a URL

The following code does steps 1 and 2 in rapid succession:

my %input = (
    "NaMe" => "Fred",
    "iD" => "123",
    "PET" => "Cat",
    "spoon" => "garbage",
);
my %caseCorrection =
(
    "name" => "Name",
    "id" => "ID",
    "pet" => "pet",
);
my %output;
%output = map {
        $caseCorrection{lc $_} => $input{$_}
    } grep {
        exists $caseCorrection{lc $_}
    } keys %input;

my $getString = join ";", map {
        "$_=$output{$_}"
    } keys %output;
[download]

The above doesn't handle:

• Input keys which only differ by case. eg (id => 1, ID => 2)
• Encoding significant characters in the URL, eg "=" -> "%61"

Depending on what else is going on before this point, these may be non-issues.

It now occurs to me that I've not used the CGI module anywhere. I hope I've been barking up the right tree...