The server my site is on cannot use curl, wget or lynx to call the external cron address (eg http://example.com/cron/cron_key)
Is it possible to use php to 'run' the cron from inside the server.
I'm was thinking something like php -f /home/docroot/core/Drupal/Cron.php with a query string for the cron key, but I notice there isn't a query string as in Drupal 7.
I cannot use Drush since it's not installed on the prod servers.
I also cannot use a third party external cron service.