You can add the custom http headers from client side to server side using the ajaxBeforeLoad event in our Report Viewer and Report Designer components. You can find the following help documentation for adding the custom http headers for the Bold Reports® Report Viewer and Report Designer.
Custom http headers for JavaScript Report Viewer
Custom http headers for ASP.NET Web Forms Report Viewer
Custom http headers for ASP.NET MVC Report Viewer
Custom http headers for ASP.NET Core Report Viewer
Custom http headers for Angular Report Viewer
Custom http headers for React Report Viewer
Custom http headers for JavaScript Report Designer
Custom http headers for ASP.NET Web Forms Report Designer
Custom http headers for ASP.NET MVC Report Designer
Custom http headers for ASP.NET Core Report Designer