AllowAllAuth.php

<?php

namespace Drupal\xxx\Authentication\Provider;

use Drupal\Core\Authentication\AuthenticationProviderInterface;
use Symfony\Component\HttpFoundation\Request;
use Drupal\Core\Session\AccountProxyInterface;

/**
 * Allow all authentication provider.
 */
class AllowAllAuth implements AuthenticationProviderInterface {

  /**
   * {@inheritdoc}
   */
  public function applies(Request $request) {
    return TRUE;
  }

  /**
   * {@inheritdoc}
   */
  public function authenticate(Request $request) {
    return $this->currentUser->getAccount();
    // return NULL;
  }

  /**
   * {@inheritdoc}
   */
  protected $currentUser;

  /**
   * {@inheritdoc}
   */
  public function __construct(AccountProxyInterface $currentUser) {
    $this->currentUser = $currentUser;
  }

}