mandrill_validate_webhook.js

var Crypto = require('crypto');

/**
 * validates a mandrill webhook request
 * @param url string the url that mandrill sent the request to
 * @param key string the web hook key from https://mandrillapp.com/settings/webhooks
 * @param params array the request's POST parameters i.e. req.params
 * @param compareTo string the x-mandrill-signature header value
 */
var validate = function validate(url, key, params, compareTo) {
  var data = url;
  for(var postKey in params) {
    data += postKey;
    data += params[postKey];
  }
  var signer = Crypto.createHmac('sha1', key);
  var signature = signer.update(data).digest('base64');
  return compareTo && signature === compareTo;
};