FileExtensionSecureConstraint.php

<?php

declare (strict_types=1);
namespace Drupal\file\Plugin\Validation\Constraint;

use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\Core\Validation\Attribute\Constraint;
use Symfony\Component\Validator\Constraint as SymfonyConstraint;

/**
 * File extension secure constraint.
 */
class FileExtensionSecureConstraint extends SymfonyConstraint {
  
  /**
   * The error message.
   *
   * @var string
   */
  public string $message = 'For security reasons, your upload has been rejected.';

}