We are implementing Telerik Reporting in our ASP.NET hosted Blazor WASM application (using .NET 6).
So far we based our implementation on the following sample: https://github.com/telerik/reporting-samples/tree/master/BlazorViewerAndDesignerExample, using a DesignerController which derives from ReportDesignerControllerBase.

As described in the following forum post, we require to add an HttpOnly Cookie to the UserIdentity.Context.
The cookie is to be used for authentication in the apicontroller of the WebServiceDataSource.
https://www.telerik.com/forums/pass-user-claimsprincipal-from-reportscontroller-to-webservice-datasource-controller 

So far we were able to add the cookie to the user context for most endpoints that request data from the WebServiceDataSource, except for a single endpoint.
The HTTP Post endpoint '/data/model' (TelerikDesignerController.GetDataModel(DataSourceInfo dsi)) can not be overriden in the derived controller class.
This causes an error when the WebServiceDataSource is used in the a report at design-time in the WebReportDesigner.

It should be possible to override all public endpoints of the ReportDesignerControllerBase in my opinion.

Also the RenderLiveItemAsync() method should be marked 'protected virtual' so it can be overridden in a derived class.
Currently we had to override every unique render method (RenderGraphAsync, RenderShapeAsync, ...) individually, while we could achieve the same if we could override the RenderLiveItemAsync method.

KR,

Lennert