How can I change the useragent and referer for javascript in IWebBrowser2 in C++

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C++

I wrote a simple C++ program that opens a test page in IE window using IWebBrowser2 with my HTML header (Referer, UserAgent). Everything works fine. PHP functions on the test page show the modified headers. However, Javascript (document.referrer, navigator.userAgent) does not. How to set referer and useragent for Javascript in IWebBrowser2 IE window?

This is my program:

#include <windows.h>
#include <Exdisp.h>

int main(){
	if (SUCCEEDED(OleInitialize(NULL))){
		IWebBrowser2* wb;

		CoCreateInstance(CLSID_InternetExplorer, NULL, CLSCTX_LOCAL_SERVER, IID_IWebBrowser2, (void**)&wb);
	   
		if(wb){
			VARIANT vempty;
			VariantInit(&vempty);

			VARIANT vheaders = { 0 };
			BSTR headers = SysAllocString( L"Referer: http://example.com\r\nUser-Agent: xyz\r\n" );
			V_VT( &vheaders ) = VT_BSTR;
			V_BSTR( &vheaders ) = headers;

			BSTR url = SysAllocString(L"http://localhost/test2.php");

			HRESULT hr = wb->Navigate(url, &vempty, &vempty, &vempty, &vheaders);
		   
			if(SUCCEEDED(hr)){
				wb->put_Visible(VARIANT_TRUE);
			}
			else{
			   wb->Quit();
			}

			SysFreeString(url);
			SysFreeString(headers);
			wb->Release();
		}

		OleUninitialize();
	}

	system("PAUSE");
}