Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/modules/system/src/Access/CronAccessCheck.php

@@ -0,0 +1,38 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\Access\CronAccessCheck.
+ */
+
+namespace Drupal\system\Access;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Routing\Access\AccessInterface;
+
+/**
+ * Access check for cron routes.
+ */
+class CronAccessCheck implements AccessInterface {
+
+  /**
+   * Checks access.
+   *
+   * @param string $key
+   *   The cron key.
+   *
+   * @return \Drupal\Core\Access\AccessResultInterface
+   *   The access result.
+   */
+  public function access($key) {
+    if ($key != \Drupal::state()->get('system.cron_key')) {
+      \Drupal::logger('cron')->notice('Cron could not run because an invalid key was used.');
+      return AccessResult::forbidden()->setCacheMaxAge(0);
+    }
+    elseif (\Drupal::state()->get('system.maintenance_mode')) {
+      \Drupal::logger('cron')->notice('Cron could not run because the site is in maintenance mode.');
+      return AccessResult::forbidden()->setCacheMaxAge(0);
+    }
+    return AccessResult::allowed()->setCacheMaxAge(0);
+  }
+}