function (user, context, callback) {
    // We check users only authenticated with 'github'
    if(context.connection === 'github'){

      var whitelist = [
        'bcoe',
        'batman'
      ]; //authorized github accounts.
      var userHasAccess = whitelist.some((name) => {
        return name === user.nickname;
      });

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

    callback(null, user, context);
}