How do I access the get mode parameters from an ISAPI *filter* (not
extension) in Visual C++ 6.0?   For example, with the URL
  http://mysite.com/index.php?abc=123

I am looking for the "abc=123" part.  

Ideally, I need to access the parameters from the function:

DWORD CMyClass::OnPreprocHeaders(CHttpFilterContext* pCtxt,
PHTTP_FILTER_PREPROC_HEADERS pHeaderInfo)

I can read the URL by doing:
  pHeaderInfo->GetHeader(pCtxt->m_pFC, "url", szUrl, &dwUrlSize);

And the cookies by doing:
  pHeaderInfo->GetHeader(pCtxt->m_pFC, "Cookie:", szCookie,
&dwCookieSize);

Thanks!