Christopher R. Palmer made it possible to build libcurl with the

USE_WINDOWS_SSPI on Windows, and then libcurl will be built to use the native
way to do NTLM. SSPI also allows libcurl to pass on the current user and its
password in the request.

lib/url.c

@@ -832,7 +832,7 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option, ...)
   {
     long auth = va_arg(param, long);
     /* switch off bits we can't support */
-#ifndef USE_SSLEAY
+#if ! defined(USE_SSLEAY) && !defined(USE_WINDOWS_SSPI)
     auth &= ~CURLAUTH_NTLM; /* no NTLM without SSL */
 #endif
 #ifndef HAVE_GSSAPI
@@ -1449,6 +1449,10 @@ CURLcode Curl_disconnect(struct connectdata *conn)
       data->state.authhost.want;
 
     data->state.authproblem = FALSE;
+
+#if defined(USE_SSLEAY) || defined(USE_WINDOWS_SSPI)
+    Curl_ntlm_cleanup(conn);
+#endif
   }
 
   if(conn->curl_disconnect)