title: symfony 2 how to display the error after login with custom authentication handler
body: <p>I have created an authentication handler and everything is working fine when the user authenticates with success...but when there is a failure I don't know how to return the failure error to my form and display it.</p>
  
  <pre><code>public function onAuthenticationFailure(Request $request, AuthenticationException $exception)
  {
  }
  </code></pre>
  
  <p>How should my function look like because I do not know how to pass $exception and redirect back to my form.</p>