winhttp: properly support ntlm and negotiate

When parsing unauthorized responses, properly parse headers looking for
both NTLM and Negotiate challenges.  Set the HTTP credentials to default
credentials (using a `NULL` username and password) with the schemes
supported by ourselves and the server.

src/transports/winhttp.c

@@ -172,9 +172,15 @@ static int apply_default_credentials(HINTERNET request, int mechanisms)
 	 * is "medium" which applies to the intranet and sounds like it would correspond
 	 * to Internet Explorer security zones, but in fact does not. */
 	DWORD data = WINHTTP_AUTOLOGON_SECURITY_LEVEL_LOW;
+	DWORD native_scheme = 0;
 
-	if ((mechanisms & GIT_WINHTTP_AUTH_NTLM) == 0 &&
-		(mechanisms & GIT_WINHTTP_AUTH_NEGOTIATE) == 0) {
+	if ((mechanisms & GIT_WINHTTP_AUTH_NTLM) != 0)
+		native_scheme |= WINHTTP_AUTH_SCHEME_NTLM;
+
+	if ((mechanisms & GIT_WINHTTP_AUTH_NEGOTIATE) != 0)
+		native_scheme |= WINHTTP_AUTH_SCHEME_NEGOTIATE;
+
+	if (!native_scheme) {
 		giterr_set(GITERR_NET, "invalid authentication scheme");
 		return -1;
 	}
@@ -182,6 +188,9 @@ static int apply_default_credentials(HINTERNET request, int mechanisms)
 	if (!WinHttpSetOption(request, WINHTTP_OPTION_AUTOLOGON_POLICY, &data, sizeof(DWORD)))
 		return -1;
 
+	if (!WinHttpSetCredentials(request, WINHTTP_AUTH_TARGET_SERVER, native_scheme, NULL, NULL, NULL))
+		return -1;
+
 	return 0;
 }
 
@@ -606,12 +615,12 @@ static int parse_unauthorized_response(
 	if (WINHTTP_AUTH_SCHEME_NTLM & supported) {
 		*allowed_types |= GIT_CREDTYPE_USERPASS_PLAINTEXT;
 		*allowed_types |= GIT_CREDTYPE_DEFAULT;
-		*allowed_mechanisms = GIT_WINHTTP_AUTH_NEGOTIATE;
+		*allowed_mechanisms |= GIT_WINHTTP_AUTH_NTLM;
 	}
 
 	if (WINHTTP_AUTH_SCHEME_NEGOTIATE & supported) {
 		*allowed_types |= GIT_CREDTYPE_DEFAULT;
-		*allowed_mechanisms = GIT_WINHTTP_AUTH_NEGOTIATE;
+		*allowed_mechanisms |= GIT_WINHTTP_AUTH_NEGOTIATE;
 	}
 
 	if (WINHTTP_AUTH_SCHEME_BASIC & supported) {