The Reporting REST WebAPI based Service is a controller for which you can enable CORS
. The linked article is an external tutorial describing the required Nuget packages, and the settings for the Reporting REST service's project.
If you use Telerik Report Server, it is configured for CORS. The viewer calling the Report Server should be of the same version as the Report Server e.g., Report Server 220.127.116.115 corresponds to v10.2.16.1025 of Telerik Reporting and its resources like HTML5 Viewer. Report Server R1 2017 is expected in March.
I hope this helps.
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