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WSO2 Message Broker (WSO2 MB) uses two transport protocols for the purpose of brokering messages between publishers and subscribers. These protocols are the Advanced Message Queueing Protocol (AMQP) and the Message Queueing and Telemetry Transport (MQTT).

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Message Queueing and Telemetry Transport

The Message Queueing and Telemetry Transport (MQTT) is a lightweight, broker-based publish/subscribe messaging protocol, which enables an extremely lightweight publish/subscribe messaging model. WSO2 MB 3.0.0 and later versions fully support MQTT version 3.1.0, and partially supports version 3.1.1.

The MQTT protocol allows a message to be sent to a topic based on three levels of QoS (Quality of Service) as explained below.

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<mqtt enabled="true">
	..............
    <security>
             <authentication>OPTIONAL</authentication>
             <authenticator>org.wso2.carbon.andes.authentication.andes.CarbonBasedMQTTAuthenticator</authenticator>
			 <!--authenticator class="org.wso2.carbon.andes.authentication.andes.OAuth2BasedMQTTAuthenticator">
                <property name="hostURL">https://localhost:9443/services/OAuth2TokenValidationService</property>
				<property name="username">admin</property>
				<property name="password">admin</property>
				<property name="maxConnectionsPerHost">10</property>
				<property name="maxTotalConnections">150</property>
			</authenticator-->
			<authorization>NOT_REQUIRED</authorization>
			<authorizer class="org.wso2.carbon.andes.authorization.andes.CarbonPermissionBasedMQTTAuthorizer">
				<property name="connectionPermission">/permission/admin/mqtt/connect</property>
			</authorizer>
    </security>
</mqtt>

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The above configuations are explained below: 

• Anchor
  authentication authentication

  The <authentication> element instructs the MQTT server on whether clients should always send credentials when establishing a connection. Possible values are as follows:

  OPTIONAL	This is the default value. If an MQTT client sends credentials, the server will validate them. If the client does not send credentials, the server will allow the client to establish the connection without authentication. This behavior adheres to the MQTT 3.1 specification.
  REQUIRED	If the MQTT client doesn't send credentials or if the credentials are invalid, the server will reject the connection.

• The <authenticator> element specifies the class that implements authentication. By default, the org.wso2.carbon.andes.authentication.andes.CarbonBasedMQTTAuthenticator class is enabled, which authenticates the user's credentials against the carbon user store.

  If required, you can disable the default authenticator and enable the org.wso2.carbon.andes.authentication.andes.OAuth2BasedMQTTAuthenticator authenticator class as shown below. This class enables OAuth-based authentication and authorization for MQTT.

  Code Block
  language xml
  <mqtt enabled="true"> .............. <security> ......... <authenticator class="org.wso2.carbon.andes.authentication.andes.OAuth2BasedMQTTAuthenticator"> <property name="hostURL">https://localhost:9443/services/OAuth2TokenValidationService</property> <property name="username">admin</property> <property name="password">admin</property> <property name="maxConnectionsPerHost">10</property> <property name="maxTotalConnections">150</property> </authenticator> ...... </security> </mqtt>

• Anchor
  authorization authorization

  The <authorization> element instructs the MQTT server on whether clients should have permission to publish messages to the broker or to subscribe to the broker. Possible values are as follows:

  NOT_REQUIRED	This is the default value. The MQTT client does not require permission for the purpose of publishing messages or to subscribe.
  REQUIRED	The permissions granted to the MQTT client will be checked before allowing the client to publish messages. This check will execute the class given in the <authorizer> element that is explained below. Note that the <authentication> element should be set to REQUIRED for authorization to be REQUIRED.

• Anchor
  authorizer authorizer

  The <authorizer> element specifies the permissions required by a user to connect to the broker. This is applicable if the <authorization> element is set to REQUIRED.

  Code Block
  language xml
  <mqtt enabled="true"> .............. <security> ........ <authorizer class="org.wso2.carbon.andes.authorization.andes.CarbonPermissionBasedMQTTAuthorizer"> <property name="connectionPermission">/permission/admin/mqtt/connect</property> </authorizer> </security> </mqtt>