Security/Authentication/AuthenticationFailureHandler.php
public function onAuthenticationFailure(Request $request, AuthenticationException $exception)
    {
        if (($request->get('_format') == 'json'
            || 0 < strpos($request->headers->get('accept'), 'application/json')
            || 0 < strpos($request->headers->get('accept'), 'text/javascript'))
        ) {
            return new JsonErrorResponse('Authentication failed. Please try again.');
        }

        return parent::onAuthenticationFailure($request, $exception);
    }
public function onAuthenticationFailure(Request $request, AuthenticationException $exception)
    {
        if (($request->get('_format') == 'json'
            || 0 < strpos($request->headers->get('accept'), 'application/json')
            || 0 < strpos($request->headers->get('accept'), 'text/javascript'))
        ) {
            return new JsonErrorResponse('Authentication failed. Please try again.');
        }

        return parent::onAuthenticationFailure($request, $exception);
    }
{@inheritDoc}