Drush cron - how to provide the actual task
From the Drupal perspective, you just need to implement hook_cron():

function MYMODULE_cron() {
  drupal_http_request('http://foo.bar');
}


That will be invoked on all normal cron runs (there are situations when it won't, e.g. if you have a cron management module installed that limits core cron operations).

But it might make more sense just to wget/curl that URL on a separate single-line cron job. Depends on your use case, but either will probably be fine.