code: function authenticate(username, password) {
      console.log('Authenticating as ' + username);
      return username.split('').reverse().join('') === password;
  }
docs: To authenticate using PLAIN and a simple username and password
  combination, the application provides a callback function for
  authenticating a connecting user given their specified username and
  password. (The test used here - namely that the password is always
  the username in reverse - is of course NOT recommended in practice!
  :-)