add this header to any url requests from this browser
public static void AddHeader(HHTMLBrowser unBrowserHandle, string pchKey, string pchValue) { InteropHelp.TestIfAvailableClient(); using (var pchKey2 = new InteropHelp.UTF8StringHandle(pchKey)) using (var pchValue2 = new InteropHelp.UTF8StringHandle(pchValue)) { NativeMethods.ISteamHTMLSurface_AddHeader(unBrowserHandle, pchKey2, pchValue2); } }