I posted the same question a month ago about the IAccessDeniedHandler and got to a dead end with it.
What are you trying to achieve? What conditions will trigger the user to be redirected to your access denied page?
Essentially, I'm running some custom logic to check for the existence of a session variable as well as a few bits of logic around a page's access control list. If that custom logic returns false, I want to force the user to be redirected to a custom URL, not the default Optimizely login URL -- which is triggered now because the page does not give "everyone" access via the Access Viewer.
I was previously running this logic in the OnAuthorization event handler with my PageControllerBase, but that has since been removed as well in .NET Core.
In which case you might benefit from implementing the IAuthorizationMiddlewareResultHandler.
I blogged about a similiar situation where I wanted the user to be redirected to different login path based what resource they were trying to access:
I'm looking to serve up a custom access denied page for specific pages in the CMS, one that does not redirect to the default Optimizely CMS login screen. Previously, I would have implemented a custom IAccessDeniedHandler, but it appears that interface is only available in the Episerver.CMS.AspNet, which cannot be used.
Is there a .NET Core equivalent or should I be approaching this a different way?