email.js

function (user, context, callback) {
  if (context.clientName !== 'YOURAPPNAME') {
    return callback(null, user, context);
  }

  var whitelist = ['info@example.com', 'owner@example.org']; //authorized emails
  var userHasAccess = whitelist.some(
    function (email) {
      return user.email.toLowerCase() === email;
    });

  if (!userHasAccess) {
    return callback(new UnauthorizedError('Access denied.'));
  }

  return callback(null, user, context);
}