Add `mosquitto_ssl_get()`.

This allow clients to access their SSL structure and
perform additional verification.

ChangeLog.txt

@@ -37,6 +37,8 @@ Client library:
   setting the retain bit.
 - Added MOSQ_OPT_TCP_NODELAY, to allow disabling Nagle's algorithm on client
   sockets. Closes #1526.
+- Add `mosquitto_ssl_get()` to allow clients to access their SSL structure and
+  perform additional verification.
 
 Clients:
 - Add timeout return code (27) for `mosquitto_sub -W <secs>` and

lib/linker.version

@@ -138,4 +138,5 @@ MOSQ_1.7 {
 		mosquitto_property_identifier;
 		mosquitto_property_identifier_to_string;
 		mosquitto_property_next;
+		mosquitto_ssl_get;
 } MOSQ_1.6;

lib/mosquitto.h

@@ -1743,6 +1743,23 @@ libmosq_EXPORT int mosquitto_tls_opts_set(struct mosquitto *mosq, int cert_reqs,
 libmosq_EXPORT int mosquitto_tls_psk_set(struct mosquitto *mosq, const char *psk, const char *identity, const char *ciphers);
 
 
+/*
+ * Function: mosquitto_ssl_get
+ *
+ * Retrieve a pointer to the SSL structure used for TLS connections in this
+ * client. This can be used in e.g. the connect callback to carry out
+ * additional verification steps.
+ *
+ * Parameters:
+ *  mosq - a valid mosquitto instance
+ *
+ * Returns:
+ *  A valid pointer to an openssl SSL structure - if the client is using TLS.
+ *  NULL - if the client is not using TLS, or TLS support is not compiled in.
+ */
+libmosq_EXPORT void *mosquitto_ssl_get(struct mosquitto *mosq);
+
+
 /* ======================================================================
  *
  * Section: Callbacks

lib/net_mosq.c

@@ -1174,3 +1174,14 @@ int net__socketpair(mosq_sock_t *pairR, mosq_sock_t *pairW)
 #endif
 }
 #endif
+
+#ifndef WITH_BROKER
+void *mosquitto_ssl_get(struct mosquitto *mosq)
+{
+#ifdef WITH_TLS
+	return mosq->ssl;
+#else
+	return NULL;
+#endif
+}
+#endif