AWS4 Signing via Postman

var datetime = (new Date()).toISOString().replace(/[:\-]|\.\d{3}/g, '');

var req = buildRequest(pm.environment.get('ESHost'), request.data);

pm.environment.set('authorization', req.headers.Authorization);
pm.environment.set('xAmzDate', datetime);

function buildRequest(endpoint, body) {
  var endpointParts = endpoint.match(/^([^\.]+)\.?([^\.]*)\.?([^\.]*)\.amazonaws\.com$/);
  var region = endpointParts[2];
  var service = endpointParts[3];
  //var datetime = (new Date()).toISOString().replace(/[:\-]|\.\d{3}/g, '');
  var date = datetime.substr(0, 8);
  var kDate = hmac('AWS4' + pm.globals.get('secret_key'), date);
  var kRegion = hmac(kDate, region);
  var kService = hmac(kRegion, service);
  var kSigning = hmac(kService, 'aws4_request');

  var request = {
    host: endpoint,
    method: 'POST',
    path: '/myindex/_doc/_search',
    body: body,
    headers: {
      'Content-Type': 'application/json',
      'Host': endpoint,
      'Content-Length': Buffer.byteLength(body),
      'X-Amz-Date': datetime
    }
  };

  var canonicalHeaders = Object.keys(request.headers)
    .sort(function(a, b) { return a.toLowerCase() < b.toLowerCase() ? -1 : 1; })
    .map(function(k) { return k.toLowerCase() + ':' + request.headers[k]; })
    .join('\n');
  console.log('canonicalHeaders='+canonicalHeaders);

  var signedHeaders = Object.keys(request.headers)
    .map(function(k) { return k.toLowerCase(); })
    .sort()
    .join(';');
  console.log('signedHeaders='+signedHeaders);

  var canonicalString = [
    request.method,
    request.path, '',
    canonicalHeaders, '',
    signedHeaders,
    hash(request.body),
  ].join('\n');
  console.log('canonicalString='+canonicalString);

  var credentialString = [ date, region, service, 'aws4_request' ].join('/');

  var stringToSign = [
    'AWS4-HMAC-SHA256',
    datetime,
    credentialString,
    hash(canonicalString)
  ] .join('\n');

  request.headers.Authorization = [
    'AWS4-HMAC-SHA256 Credential=' + pm.globals.get('access_key') + '/' + credentialString,
    'SignedHeaders=' + signedHeaders,
    'Signature=' + hmac(kSigning, stringToSign)
  ].join(', ');

  return request;
}

function hmac(key, str) {
  return CryptoJS.enc.Hex.stringify(CryptoJS.HmacSHA256(str, key));
}

function hash(str) {
  return CryptoJS.enc.Hex.stringify(CryptoJS.SHA256(str));
}