The IInetLogInformation::GetExtraHTTPHeaders method retrieves a NULL-separated list of parameters requested by the logging module from the Web server.
virtual LPSTR STDMETHODCALLTYPE GetExtraHTTPHeaders( IN PCHAR pszHTTPHeaders, IN PDWORD pcbSize );
Logging modules should query for this method if a server instance has set the MD_EXTLOG_COOKIE, MD_EXTLOG_USER_AGENT or MD_EXTLOG_REFERER metabase identifier.
LogExtFileCookie, LogExtFileReferer, LogExtFileUserAgent, MD_LOGEXT_FIELD_MASK