From 93712fcfbd26270b464e33860b12fed936e72e14 Mon Sep 17 00:00:00 2001
From: Saksik Remy <rsaksik@gemalto.com>
Date: Mon, 20 Dec 2021 17:34:27 +0800
Subject: [PATCH] fallback in software imp if callback not supporting operation
 ie: NULL salt

---
 src/tls13.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/tls13.c b/src/tls13.c
index 08e2adefb..7fbad0502 100644
--- a/src/tls13.c
+++ b/src/tls13.c
@@ -860,6 +860,11 @@ static int Tls13_HKDF_Extract(WOLFSSL *ssl, byte* prk, const byte* salt, int sal
     CallbackHKDFExtract cb = ssl->ctx->HkdfExtractCb;
     if (cb != NULL) {
         ret = cb(prk, salt, saltLen, ikm, ikmLen, digest, cb_ctx);
+        if(ret == NOT_COMPILED_IN)
+        {
+            WOLFSSL_MSG("Not supported by callback, fallback to software implementation");
+            ret = wc_Tls13_HKDF_Extract(prk, salt, saltLen, ikm, ikmLen, digest);
+        }
     }
     else
 #endif