In this recipe, we will look at adding callbacks or webhooks into your API. Webhooks are a method of using custom callbacks to alter the behavior of a web application often in order to provide a capability to integrate two separate web applications. For instance, GitHub provides a webhook that will call a service you define anytime someone forks your code—you might take advantage of them by creating an API that receives notifications when someone forks your code. You provide the service that GitHub calls, and GitHub makes sure to call your service any time that happens.

We will be focusing how to get this going using filter attributes so that you are also able to control which of your web services allows these callbacks. This technique can be useful for developers writing APIs for longer-running tasks...