use LWP::UserAgent;
use JSON;
use Digest::MD5 qw(md5);
use Digest::SHA qw(hmac_sha256_base64);
use MIME::Base64;

my $api_key ='PUBLIC KEY';
my $api_private_key ='PRIVATE KEY';
my $ua = LWP::UserAgent->new;

my $url = "https://www.cryptopia.co.nz/api/GetBalance";

my %req = (
    Currency => "PAC"
);

my $nonce = int(rand(1000000));
my $post_data = encode_json(\%req);
my $post_data_enc = encode_base64(md5($post_data));
my $req_signature = sprintf("%sPOST%s%s%s", $api_key, lc(urlencode($url)), $nonce, $post_data_enc);
# Sign request signature with private key.
my $req_signature_hmac = hmac_sha256_base64($req_signature, decode_base64($api_private_key));
# Generate value for 'Authorization' header field.
my $auth_header_value = sprintf("amx %s:%s:%s", $api_key, $req_signature_hmac, $nonce);
my $response = $ua->post($url,
    Content => $post_data,
    'Content-Type' => 'application/json',
    'charset' => 'utf-8',
    Authorization => $auth_header_value
);

die "Request failed: ", $response->content unless $response->is_success();

print $response->content, $/;
sub urlencode {
    my $s = shift;
    $s =~ s/ /+/g;
    $s =~ s/([^A-Za-z0-9\+-])/sprintf("%%%02X", ord($1))/seg;
    return $s;
}