@@ -1071,11 +1071,11 @@
     const unsigned char *session_id = NULL;
     Tcl_Obj *alpn		= NULL;
     int ssl2 = 0, ssl3 = 0;
     int tls1 = 1, tls1_1 = 1, tls1_2 = 1, tls1_3 = 1;
     int proto = 0, level = -1;
-    int verify = 0, require = 0, request = 1;
+    int verify = 0, require = 0, request = 1, post_handshake = 0;
 
     dprintf("Called");
 
 #if OPENSSL_VERSION_NUMBER < 0x10100000L && !defined(OPENSSL_NO_SSL2) && !defined(NO_SSL2) && defined(NO_SSL3) && defined(NO_TLS1) && defined(NO_TLS1_1) && defined(NO_TLS1_2) && defined(NO_TLS1_3)
     ssl2 = 1;
@@ -1124,10 +1124,11 @@
 	OPTOBJ("-command", script);
 	OPTSTR("-dhparams", DHparams);
 	OPTSTR("-keyfile", keyfile);
 	OPTSTR("-model", model);
 	OPTOBJ("-password", password);
+	OPTBOOL("-post_handshake", post_handshake);
 	OPTBOOL("-require", require);
 	OPTBOOL("-request", request);
 	OPTINT("-securitylevel", level);
 	OPTBOOL("-server", server);
 	OPTSTR("-servername", servername);
@@ -1146,10 +1147,11 @@
 
 	return TCL_ERROR;
     }
     if (request)	    verify |= SSL_VERIFY_CLIENT_ONCE | SSL_VERIFY_PEER;
     if (request && require) verify |= SSL_VERIFY_FAIL_IF_NO_PEER_CERT;
+    if (request && post_handshake)  verify |= SSL_VERIFY_POST_HANDSHAKE;
     if (verify == 0)	verify = SSL_VERIFY_NONE;
 
     proto |= (ssl2 ? TLS_PROTO_SSL2 : 0);
     proto |= (ssl3 ? TLS_PROTO_SSL3 : 0);
     proto |= (tls1 ? TLS_PROTO_TLS1 : 0);
@@ -1361,17 +1363,27 @@
 	/* Server callbacks */
 	SSL_CTX_set_alpn_select_cb(statePtr->ctx, ALPNCallback, (void *)statePtr);
 	SSL_CTX_set_tlsext_servername_arg(statePtr->ctx, (void *)statePtr);
 	SSL_CTX_set_tlsext_servername_callback(statePtr->ctx, SNICallback);
 	SSL_CTX_set_client_hello_cb(statePtr->ctx, HelloCallback, (void *)statePtr);
+
+	/* Enable server to send cert request after handshake (TLS 1.3 only) */
+	if (request && post_handshake) {
+	    SSL_verify_client_post_handshake(statePtr->ssl);
+	}
 
 	statePtr->flags |= TLS_TCL_SERVER;
 	SSL_set_accept_state(statePtr->ssl);
     } else {
 	/* Session caching */
 	SSL_CTX_set_session_cache_mode(statePtr->ctx, SSL_SESS_CACHE_CLIENT | SSL_SESS_CACHE_NO_INTERNAL_STORE);
 	SSL_CTX_sess_set_new_cb(statePtr->ctx, SessionCallback);
+
+	/* Enable post handshake Authentication extension. TLS 1.3 only, not http/2. */
+	if (request && post_handshake) {
+	    SSL_set_post_handshake_auth(statePtr->ssl, 1);
+	}
 
 	SSL_set_connect_state(statePtr->ssl);
     }
     SSL_set_bio(statePtr->ssl, statePtr->p_bio, statePtr->p_bio);
     BIO_set_ssl(statePtr->bio, statePtr->ssl, BIO_NOCLOSE);