UPDATED on Oct 17, 2013: If your POST data is in JSON format, SetCronJob automatically appends a header Content-Type: application/json to the POST request.
SetCronJob is a web based cronjob service, and it works with URL only. By default SetCronJob will make your script execute by sending a GET request to its URL.
After receiving many feature requests to POST support, we had considered and finally added POST requests to our cronjob service.
To send a POST request to your cron URL, just hit More options, then enter POST data with format
For example, to log in to SetCronJob, enter cron URL
and POST data
If the POST data is empty (by default), SetCronJob will obviously send GET request as usual.
You can read more about POST and GET at HTTP Methods: GET vs. POST.