Azure Websites: Blocking access to the azurewebsites.net url

I’ve been setting up one of our services as the backend service for Azure API management. Part of this process we have mapped DNS to point to the service. As the service is hosted in Azure Websites there are now two urls that exist which can be used to access the service. I wanted to stop a user from accessing the site using the azurewebsites.net url and only access it via the mapped domain. This is easy to achieve and can be configured in the web.config file of the service.

In the <system.webServer> section add the following configuration

Now if I try and access my site through the azurewebsites.net url, I get a 403 error, but accessing through the mapped domain is fine.