Response|null onAuthenticationFailure(Request $request, AuthenticationException $exception)
Called when authentication executed, but failed (e.g. wrong username password).
This should return the Response sent back to the user, like a RedirectResponse to the login page or a 403 response.
If you return null, the request will continue, but the user will not be authenticated. This is probably not what you want to do.
Please login to continue.