Event Handlers are a system of callouts in the AspDotNetStorefront software that can post information to endpoint URLs (such as an app that accepts the calls, processes the data, and then calls the WSI )when certain events happen on the site, making integration with 3rd-party applications easier. The software has several handlers built in, and store admins with the source code can add new events if desired.
This is an advanced tool and will require a developer to set up. Stores without source code access will only be able to use the built-in handlers. Please note that Event Handlers will not function in medium trust hosting environments!
Also, please be aware that when creating a listener page to consume the posts made by EventHandlers, you must disable validation on the page if it is written in .NET. EventHandlers post XML-formatted data, which .NET's validation flags as invalid/unsafe.
Built in Event Handlers
From the Configuration menu, click EventHandler Configuration. AspDotNetStorefront includes 10 EventHandlers by default, but a developer with access to AspDotNetStorefront source code can add an unlimited number of events.
To enable an event handler, click the Edit button, check the Active checkbox, and specify a callback URL.
The URL specified for the callback is a separate URL that a developer must create, this is running outside of the AspDotNetStorefront software. The real value of such a solution is that many custom features can be removed from core, making the upgrade process easier.