Promisified function for validating the user agent of an AWS Lambda invocation

validateUserAgent.js

function validateUserAgent(event, desiredUserAgent) {

  return new Promise(function(resolve, reject) {
    const foundUserAgent = event.requestContext.identity.userAgent.toLowerCase();

    if (foundUserAgent.startsWith(desiredUserAgent.toLowerCase())) {
      resolve(querystring.parse(event.body));
    } else {
      reject(buildError(401, "This endpoint cannot be accessed via the current User Agent."));
    }

  });
  
}