PayKickStart IPN POST Checksum Verification in JavaScript

PayKickStart.js

function verifyChecksum (params, secret) {
  const valuesArray = Object
    .keys(params)
    .filter((key) => key && params[key] && key !== 'verification_code')
    .map((key) => params[key])

  const valuesObject = {}
  for (let i = 0; i < valuesArray.length; i++) {
    // stringify indexes for ASCII sort
    valuesObject[i.toString()] = valuesArray[i]
  }

  const string = Object
    .keys(valuesObject)
    .sort()
    // now access the array by actual numerical index
    .map((key) => valuesArray[parseInt(key)])
    .join('|')

  const checksum = sha1(string, secret)

  log.info('Checksum string %s == %s: %s', checksum, params.verification_code, string)

  return checksum === params.verification_code
}

function sha1 (string, secret) {
  const hmac = crypto.createHmac('sha1', secret)
  return hmac.update(Buffer.from(string, 'utf-8')).digest('hex')
}