Amazon MWS Signature mismatch in Google Sheet - google-apps-script

Question

I am creating a Google Sheet add-on wherein I am downloading the FBA Orders. I have been trying to make a successful API call. Am I perhaps missing something here?
Response I am getting:
The request signature we calculated does not match the signature you provided. Check your AWS Secret Access Key and signing method. Consult the service documentation for details.
Google Sheet JavaScript code:
function POSTRequest() {
var config = amazonMWSConfigProperties.getProperty('amazonConfig');
var configData = JSON.parse(config);
var sellerID=configData.sellerID;
var accessKey=configData.accessKey;
var secretKey=configData.secretKey;
var authToken=configData.authToken;
var defaultMarket=configData.defaultMarket;
var url = 'https://mws.amazonservices.in/Orders/2013-09-01?';
var today1 = new Date();
var today = new Date();
var todayTime = Utilities.formatDate(today, "GMT", "yyyy-MM-dd'T'HH:mm:ss'Z'");
var yesterday = new Date();
yesterday.setDate(today.getDate() - 1);
yesterday.setHours(0,0,0,0);
var yesterdayTime = Utilities.formatDate(yesterday, "GMT", "yyyy-MM-dd'T'HH:mm:ss'Z'");
var dayBeforeYesterday = new Date();
dayBeforeYesterday.setDate(today.getDate() - 2);
dayBeforeYesterday.setHours(0,0,0,0);
var dayBeforeYesterdayTime = Utilities.formatDate(dayBeforeYesterday, "GMT", "yyyy-MM-dd'T'HH:mm:ss'Z'");
var unsignedURL =
'POST\nmws.amazonservices.in\n/Orders/2013-09-01\n'+
'AWSAccessKeyId=' +accessKey+
'&Action=ListOrders'+
'&CreatedAfter='+encodeURIComponent(Utilities.formatDate(new Date(), "GMT", "yyyy-MM-dd'T'HH:mm:ss'Z'")) +
//'&CreatedBefore=2020-01-18T18%3A30%3A00Z' + //yesterdayTime +
'&FulfillmentChannel.Channel.1=AFN' +
'&MWSAuthToken=' +authToken+
'&MarketplaceId.Id.1=' +defaultMarket+
'&SellerId='+sellerID+
'&SignatureMethod=HmacSHA256'+
'&SignatureVersion=2'+
'&Timestamp='+encodeURIComponent(Utilities.formatDate(today1, "GMT", "yyyy-MM-dd'T'HH:mm:ss'Z'")) +
'&Version=2013-09-01';
Logger.log(unsignedURL);
var SignedRequest = calculatedSignature(unsignedURL, secretKey);
var Encoded = Utilities.base64Encode(SignedRequest);
var param = 'AWSAccessKeyId=' +accessKey+
'&Action=ListOrders'+
'&CreatedAfter='+encodeURIComponent(Utilities.formatDate(new Date(), "GMT", "yyyy-MM-dd'T'HH:mm:ss'Z'")) +
//'&CreatedBefore=2020-01-18T18%3A30%3A00Z' + //yesterdayTime +
'&FulfillmentChannel.Channel.1=AFN' +
'&MWSAuthToken=' +authToken+
'&MarketplaceId.Id.1=' +defaultMarket+
'&SellerId='+sellerID+
'&Signature='+encodeURIComponent(SignedRequest) +
'&SignatureMethod=HmacSHA256'+
'&SignatureVersion=2'+
'&Timestamp='+encodeURIComponent(Utilities.formatDate(today1, "GMT", "yyyy-MM-dd'T'HH:mm:ss'Z'")) +
'&Version=2013-09-01';
Logger.log(url+param);
var result = UrlFetchApp.fetch(url+param);
//writeDataToXML(result);
Logger.log(result);
if (result.getResponseCode() == 200) {
//writeDataToXML(result);
}
}
function calculatedSignature(url,secret) {
var urlToSign = url;
var byteSignature = Utilities.computeHmacSha256Signature(urlToSign, secret);
// convert byte array to hex string
var signature = byteSignature.reduce(function(str,chr){
chr = (chr < 0 ? chr + 256 : chr).toString(16);
return str + (chr.length==1?'0':'') + chr;
},'');
//Logger.log("URL to sign: " + urlToSign);
//Logger.log("");
//Logger.log("byte " + byteSignature);
//Logger.log("");
//Logger.log("reg " + signature);
var byte64 = Utilities.base64Encode(byteSignature)
//Logger.log("base64 byte " + Utilities.base64Encode(byteSignature));
//Logger.log("");
//Logger.log("base64 reg " + Utilities.base64Encode(signature));
Logger.log("base64 reg " + byte64)
return byte64;
}

Answer 1

In addition to using the built-in encodeURIComponent, I have found that you also have to manually replace certain values. This is the function that I use to encode my URL:
/**
* Performs URL encoding compatible with MWS http requests
* #param {String} The string to encode
*/
function urlEncode(str) {
str = encodeURIComponent(str);
str = str.replace(/\*/g, '%2A');
str = str.replace(/\(/g, '%28');
str = str.replace(/\)/g, '%29');
str = str.replace(/'/g, '%27');
str = str.replace(/\!/g, '%21');
return str;
}
I call it in my createSignature function:
function createSignature(value, key) {
var signature = Utilities.computeHmacSha256Signature(value, key);
return urlEncode(Utilities.base64Encode(signature));
}
Which I call on my unsigned URL, passing my secret as the key.
I hope that helps!