If you don't want to have your own broker, but you want a secure MQTT connection you can use a cloud MQTT instance, such as http://iotcentral.eu.

First create an account on iotcentral.eu and confirm your email address. After that you can log in to iotcental.eu and get your private assigned topic. It is an eight character code, such as c5c05211, and this code needs to precede all of your topics as follows:

c5c05211/living/temperature

No matter if you publish or subscribe. The following code connects to the Wi-Fi and then establishes a secure connection to the iotcentral.eu cloud MQTT over port 8883. Every message sent to the iotcentral.eu broker is received back like a loopback.

Included header files are the ESP8266WiFi and the PubSubClient MQTT class:

#include <ESP8266WiFi.h> 
#include <PubSubClient.h> 

GPIO 12 will be used later to blink a LED every time a message is received and GPIO 13 will be changed to HIGH every time a...