POST /endpoint?user=yyy&pass=zzz HTTP/1.1
Host: api.xxx.com
Content-Type: multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW

----WebKitFormBoundary7MA4YWxkTrZu0gW

##</code><code>##

my $url = 'https://api.xxx.com/endpoint?user=yyy&pass=zzz';
my $request = HTTP::Request->new( 'POST', $url );
$request->content_type('multipart/form-data');
print $request->as_string;
my $response = $ua->request($request);
print $response->as_string;

##</code><code>##

POST https://api.xxx.com/endpoint?user=yyy&pass=zzz
Content-Type: multipart/form-data


##</code><code>##

HTTP Error 411. The request must be chunked or have a content length.