sub makeHash {
    my ($auth_key, $upc_code) = @_;

    use Digest::HMAC_SHA1 qw(hmac_sha1 hmac_sha1_hex);
    my $hmac = Digest::HMAC_SHA1->new($auth_key);
    $hmac->add($upc_code);
    my $signature = $hmac->b64digest;
    my $paddingRequired = 4-(length($signature) % 4);
    $signature .= substr("====", 0, $paddingRequired) if ($paddingRequired);
    return $signature
}