Web Hooks

https://www.youtube.com/watch?v=SzKj1knqYaw

What are Webhooks ?
Who uses Webhooks ?
How webhooks are implemented in SharePoint ?

https://docs.microsoft.com/en-us/aspnet/webhooks/

WebHooks is a lightweight HTTP pattern providing a simple pub/sub model for wiring together Web APIs and SaaS services. When an event happens in a service, a notification is sent in the form of an HTTP POST request to registered subscribers. The POST request contains information about the event which makes it possible for the receiver to act accordingly.

Because of their simplicity, WebHooks are already exposed by a large number of services including Dropbox, GitHub, Bitbucket, MailChimp, PayPal, Slack, Stripe, Trello, and many more. For example, a WebHook can indicate that a file has changed in Dropbox, or a code change has been committed in GitHub, or a payment has been initiated in PayPal, or a card has been created in Trello. The possibilities are endless!

Microsoft ASP.NET WebHooks makes it easier to both send and receive WebHooks as part of your ASP.NET application

Microsoft ASP.NET WebHooks is part of the Microsoft ASP.NET family of modules and is hosted as an Open Source Project on GitHub.

https://docs.microsoft.com/en-us/aspnet/webhooks/receiving/