If I understand your question, you can use $cgi->Vars(); to get data regardless if its a get or post. This example takes cgi input and concats them into a string for relaying elsewhere.

my $relay;
my $cgi = new CGI;
my %input= $cgi->Vars(); 
foreach $name (keys %input){
        $value = $input{$name};    
        $relay .= "$name=$value&";
         }
$relay .= "Ecom_transaction_complete=$test&";
$relay .= "IOC_response_code=0&";

open (RT,">test/respgen.test");
print RT $relay;
close RT;

my $ua = LWP::UserAgent->new();

my $req = HTTP::Request->new (POST => "$secure_server_address$cgi_dire
+ctory/boacc.pl");
$req->content_type('application/x-www-form-urlencoded');
$req->content("$relay");
my $res = $ua->request($req);
print $res->as_string;
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