SSL: add config option for skipping common name check

Closes IDFGH-3408
Closes https://github.com/espressif/esp-mqtt/issues/158

include/mqtt_client.h

@@ -182,6 +182,7 @@ typedef struct {
     int clientkey_password_len;             /*!< String length of the password pointed to by clientkey_password */
     esp_mqtt_protocol_ver_t protocol_ver;   /*!< MQTT protocol version used for connection, defaults to value from menuconfig*/
     int out_buffer_size;                    /*!< size of MQTT output buffer. If not defined, both output and input buffers have the same size defined as ``buffer_size`` */
+    bool skip_cert_common_name_check;       /*!< Skip any validation of server certificate CN field, this reduces the security of TLS and makes the mqtt client susceptible to MITM attacks  */
 } esp_mqtt_client_config_t;
 
 /**

include/mqtt_supported_features.h

@@ -31,6 +31,7 @@
 #if ESP_IDF_VERSION >= ESP_IDF_VERSION_VAL(3, 3, 0)
 // Features supported from 3.3
 #define MQTT_SUPPORTED_FEATURE_EVENT_LOOP
+#define MQTT_SUPPORTED_FEATURE_SKIP_CRT_CMN_NAME_CHECK
 #endif
 
 #if ESP_IDF_VERSION >= ESP_IDF_VERSION_VAL(4, 0, 0)
@@ -48,4 +49,4 @@
 #endif
 #endif
 
-#endif // _MQTT_SUPPORTED_FEATURES_H_
+#endif // _MQTT_SUPPORTED_FEATURES_H_