var nonce      = 1516453770998;
var API_KEY    = 'PUBLIC KEY'
var API_SECRET = 'PRIVATE KEY';

var md5 = crypto.createHash('md5').update( JSON.stringify( {'Currency':"PAC"} ) ).digest();
var requestContentBase64String = md5.toString('base64');
var signature = API_KEY + "POST" + encodeURIComponent( 'https://www.cryptopia.co.nz/api/GetBalance' ).toLowerCase() + nonce + requestContentBase64String;
var hmacsignature = crypto.createHmac('sha256', new Buffer( API_SECRET, "base64" ) ).update( signature ).digest().toString('base64');
var header_value = "amx " + API_KEY + ":" + hmacsignature + ":" + nonce;