Add support for logging TLS 1.3 exporter secret

NSS 3.34 and boringssl have support for "EXPORTER_SECRET"
(https://bugzilla.mozilla.org/show_bug.cgi?id=1287711) which is needed
for QUIC 1-RTT decryption support in Wireshark.
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5702)

ssl/ssl_locl.h

@@ -2554,6 +2554,7 @@ __owur int ssl_log_secret(SSL *ssl, const char *label,
 #define SERVER_HANDSHAKE_LABEL "SERVER_HANDSHAKE_TRAFFIC_SECRET"
 #define CLIENT_APPLICATION_LABEL "CLIENT_TRAFFIC_SECRET_0"
 #define SERVER_APPLICATION_LABEL "SERVER_TRAFFIC_SECRET_0"
+#define EXPORTER_SECRET_LABEL "EXPORTER_SECRET"
 
 /* s3_cbc.c */
 __owur char ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx);

ssl/tls13_enc.c

@@ -594,6 +594,12 @@ int tls13_change_cipher_state(SSL *s, int which)
             /* SSLfatal() already called */
             goto err;
         }
+
+        if (!ssl_log_secret(s, EXPORTER_SECRET_LABEL, s->exporter_master_secret,
+                            hashlen)) {
+            /* SSLfatal() already called */
+            goto err;
+        }
     } else if (label == client_application_traffic)
         memcpy(s->client_app_traffic_secret, secret, hashlen);
 

test/sslapitest.c

@@ -58,6 +58,7 @@ struct sslapitest_log_counts {
     unsigned int server_handshake_secret_count;
     unsigned int client_application_secret_count;
     unsigned int server_application_secret_count;
+    unsigned int exporter_secret_count;
 };
 
 
@@ -143,6 +144,7 @@ static int test_keylog_output(char *buffer, const SSL *ssl,
     unsigned int server_handshake_secret_count = 0;
     unsigned int client_application_secret_count = 0;
     unsigned int server_application_secret_count = 0;
+    unsigned int exporter_secret_count = 0;
 
     for (token = strtok(buffer, " \n"); token != NULL;
          token = strtok(NULL, " \n")) {
@@ -199,7 +201,8 @@ static int test_keylog_output(char *buffer, const SSL *ssl,
         } else if (strcmp(token, "CLIENT_HANDSHAKE_TRAFFIC_SECRET") == 0
                     || strcmp(token, "SERVER_HANDSHAKE_TRAFFIC_SECRET") == 0
                     || strcmp(token, "CLIENT_TRAFFIC_SECRET_0") == 0
-                    || strcmp(token, "SERVER_TRAFFIC_SECRET_0") == 0) {
+                    || strcmp(token, "SERVER_TRAFFIC_SECRET_0") == 0
+                    || strcmp(token, "EXPORTER_SECRET") == 0) {
             /*
              * TLSv1.3 secret. Tokens should be: 64 ASCII bytes of hex-encoded
              * client random, and then the hex-encoded secret. In this case,
@@ -214,6 +217,8 @@ static int test_keylog_output(char *buffer, const SSL *ssl,
                 client_application_secret_count++;
             else if (strcmp(token, "SERVER_TRAFFIC_SECRET_0") == 0)
                 server_application_secret_count++;
+            else if (strcmp(token, "EXPORTER_SECRET") == 0)
+                exporter_secret_count++;
 
             client_random_size = SSL_get_client_random(ssl,
                                                        actual_client_random,
@@ -254,7 +259,9 @@ static int test_keylog_output(char *buffer, const SSL *ssl,
             || !TEST_size_t_eq(client_application_secret_count,
                                expected->client_application_secret_count)
             || !TEST_size_t_eq(server_application_secret_count,
-                               expected->server_application_secret_count))
+                               expected->server_application_secret_count)
+            || !TEST_size_t_eq(exporter_secret_count,
+                               expected->exporter_secret_count))
         return 0;
     return 1;
 }
@@ -390,6 +397,7 @@ static int test_keylog_no_master_key(void)
     expected.server_handshake_secret_count = 1;
     expected.client_application_secret_count = 1;
     expected.server_application_secret_count = 1;
+    expected.exporter_secret_count = 1;
     if (!TEST_true(test_keylog_output(client_log_buffer, clientssl,
                                       SSL_get_session(clientssl), &expected))
             || !TEST_true(test_keylog_output(server_log_buffer, serverssl,