Allow signature algorithms in TLS 1.3 certificate request extensions.

Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2918)

ssl/statem/extensions.c

@@ -159,8 +159,9 @@ static const EXTENSION_DEFINITION ext_defs[] = {
     },
     {
         TLSEXT_TYPE_signature_algorithms,
-        EXT_CLIENT_HELLO,
-        init_sig_algs, tls_parse_ctos_sig_algs, NULL, NULL,
+        EXT_CLIENT_HELLO | EXT_TLS1_3_CERTIFICATE_REQUEST,
+        init_sig_algs, tls_parse_ctos_sig_algs,
+        tls_parse_ctos_sig_algs, tls_construct_ctos_sig_algs,
         tls_construct_ctos_sig_algs, final_sig_algs
     },
 #ifndef OPENSSL_NO_OCSP

ssl/statem/statem_locl.h

@@ -53,6 +53,7 @@
 #define EXT_TLS1_3_HELLO_RETRY_REQUEST      0x0400
 #define EXT_TLS1_3_CERTIFICATE              0x0800
 #define EXT_TLS1_3_NEW_SESSION_TICKET       0x1000
+#define EXT_TLS1_3_CERTIFICATE_REQUEST      0x2000
 
 /* Dummy message type */
 #define SSL3_MT_DUMMY   -1