Add support for MQTT authentication

README.md

@@ -53,7 +53,7 @@ By default, the block searches for sensors on SMBus number 1 (/dev/i2c-1) howeve
 
 ### Publishing Data
 
-The sensor data is available in json format either as an mqtt payload and/or via the built-in http server. If you include an mqtt broker container named "mqtt" in your application, the block will automatically publish to that. If you provide an address for the `MQTT_ADDRESS` service variable, it will publish to that broker instead. The default interval for publishing data is eight seconds, which you can override with the `MQTT_PUB_INTERVAL` service variable by providing a value in seconds. The default topic is set to `sensors` (which is compatible with the [connector block](https://github.com/balenablocks/connector#mqtt) ) which can be overridden by setting the `MQTT_PUB_TOPIC` service variable. 
+The sensor data is available in json format either as an mqtt payload and/or via the built-in http server. If you include an mqtt broker container named "mqtt" in your application, the block will automatically publish to that. If you provide an address for the `MQTT_ADDRESS` service variable, it will publish to that broker instead. If your MQTT broker is configured to require client authentication, you can specify a username and password by setting the `MQTT_USERNAME` and `MQTT_PASSWORD` variables. The default interval for publishing data is eight seconds, which you can override with the `MQTT_PUB_INTERVAL` service variable by providing a value in seconds. The default topic is set to `sensors` (which is compatible with the [connector block](https://github.com/balenablocks/connector#mqtt) ) which can be overridden by setting the `MQTT_PUB_TOPIC` service variable. 
 
 If no mqtt broker is set, the http server will be available on port 7575. To force the http server to be active even with mqtt, set the `ALWAYS_USE_HTTPSERVER` service variable to True.
 

sensor.py

@@ -100,6 +100,8 @@ def background_web(server_socket):
 if __name__ == "__main__":
 
     mqtt_address = os.getenv('MQTT_ADDRESS', 'none')
+    mqtt_username = os.getenv('MQTT_USERNAME', '')
+    mqtt_password = os.getenv('MQTT_PASSWORD', '')
     use_httpserver = os.getenv('ALWAYS_USE_HTTPSERVER', 0)
     publish_interval = os.getenv('MQTT_PUB_INTERVAL', '8')
     publish_topic = os.getenv('MQTT_PUB_TOPIC', 'sensors')
@@ -123,6 +125,10 @@ def background_web(server_socket):
         print("Starting mqtt client, publishing to {0}:1883".format(mqtt_address))
         print("Using MQTT publish interval: {0} sec(s)".format(interval))
         client = mqtt.Client()
+
+        if mqtt_username != "":
+            client.username_pw_set(mqtt_username, mqtt_password)
+
         try:
             client.connect(mqtt_address, 1883, 60)
         except Exception as e: