This is a basic component for configuring MQTT connections
You can set your MQTT server, username and password with idf.py menuconfig under the MQTT settings option.
From there, just import the header and call mqtt_app_start(). E.g.:
#include "scmqtt.h"
void app_main(void)
{
esp_mqtt_client_handle_t mqtt_client = mqtt_app_start();
}