code: function objectToSignature(source) {
    function sortObject(input) {
        if(typeof input !== 'object' ||input===null)
            return input
        var output = {};
         Object.keys(input).sort().forEach(function (key) {
          output[key] = sortObject(input[key]);
        });
        return output;
    }
    var signature={};
    //
    // what about transactions and transfers ??
    // FIXME append 'amount_negative',
    ['balance','card','id','wid','email','apikey'].forEach(function (key) {
      signature[key]=source[key];
    });
  
    return sortObject(signature);
  }
docs: this is used to prepare the object signature