WordPress: Catching an incoming callback from an external platform
Consumed => “A (Mostly) Complete Guide to the WordPress Rewrite API” by Christopher Davis on Performance Media Group.
As you probably already know, WordPress is strict—as it should be—about how it interprets permalink requests. If you want to deviate from that you’ve got to get acquainted with add_rewrite_rule. Or let’s say you want to catch a callback that you’ve specified on a third party platform (e.g., FileMobile.com). That is, the other platform performs some service for you and then issues a reply to a callbackURL (that you’ve specified) to let you know the task (e.g., video encoding) is completed.
The above article is probably what you’ve been looking for. I was.