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Authentication and Authorization Demo - Java Hook

The Authentication and Authorization Demo is a simple example illustrating authentication and authorization mechanisms when an external Web/Application Server is involved in the process.

This project includes simple web client front-end example and hook implementation, which supplies user validation and authorization logics.

Live Demo

Live Demo


The Authentication and Authorization Demo illustrates the typical best practice used for MQTT.Cool Web applications, when a Web/Application server is involved in the process. The actual authentication is usually handled by the legacy Web/Application server, irrespective of MQTT.Cool.

from src/web/app/Main.js:


   url: 'js/app/login.js',
   type: 'POST',
   data: {
     user: user,
     password: password

Some sort of token is sent back to the Client through cookies, response payload or any other technique. When the MQTT.Cool Web Client creates a new session, instead of sending again the full credentials (usually involving a password) to MQTT.Cool, it sends just the username and the token.

from src/web/app/Main.js:


// Now it is possible to connect to MQTT.Cool, by sending the
// token, not the password.
openSession.connect(Constants.SERVER, user, token, {


The Hook is passed this information and validates the token against the Web/Application Server that generated it (or a database or whatever back-end system).

from src/java/main/cool/mqtt/examples/auth_hooks/


AuthorizationResult result = authorizationHandler.validateToken(user, password);
if (!AuthorizationResult.OK.equals(result)) {
    throw new HookException(result.getCode(),
        "Unauthorized access: token invalid for user '" + user + "'");


Here an overview of the whole sequence:

sequence diagram

In this demo client the Web/Application server is not actually involved and calls to placeholder methods are performed to obtain and extract the token.

Once the user is authenticated on the MQTT.Cool server as explained above, the client interface presents a link by which the user can connect to the configured MQTT broker. If the user is allowed to establish a connection, two additional panels are shown, each one showing a list of topics: from the first panel, the user can request to subscribe to a topic; from the second panel, the user can request to publish a random message to a topic. In case a subscription is accepted and then submitted to the MQTT broker, incoming messages are displayed on the selected row; in case a publishing is accepted and then delivered to the MQTT broker, the user is invited to send a new one.

Every time a connection, a subscription or a publishing is requested, MQTT.Cool proceeds with the authorization check, by delegating to the Hook the responsibility to verify if the user issuing the request is actually authorized to access the resource is asking for. A real case might query an external service to verify the user authorizations; this example simply checks, for each username, on hard-coded set of permissions the following:

  • a list of contactable MQTT brokers
  • a list of subscribable topics
  • a list of topics to which messages are allowed to be delivered.

from src/java/main/cool/mqtt/examples/auth_hooks/


AuthorizationResult result =
    authorizationHandler.authorizeMQTTConnection(user, brokerAddress);
if (!AuthorizationResult.OK.equals(result)) {
    throw new HookException(result.getCode(),
        String.format("Unauthorized access: user '%s' can't connect to broker '%s'",
            user, brokerAddress));


AuthorizationResult result =
    authorizationHandler.authorizeSubscribeTo(user, subscription.getTopicFilter());
if (!AuthorizationResult.OK.equals(result)) {
    throw new HookException(result.getCode(),
        String.format("Unauthorized access: user '%s' can't receive messages from '%s'",
            user, subscription.getTopicFilter()));


AuthorizationResult result =
    authorizationHandler.authorizePublishTo(user, message.getTopicName());
if (!AuthorizationResult.OK.equals(result)) {
    throw new HookException(result.getCode(),
        String.format("Unauthorized access: user '%s' can't publish messages to '%s'",
            user, message.getTopicName()));


Querying an external service at each request is a discouraged approach, though. If the authorizations are actually placed on an external service, it is suggested to use the approach shown in the AuthHookWithAuthCache class where authorizations are queried at session startup and cached in the Hook itself.

More details and comments on how the authentication/authorization cycle is accomplished is available in the source code of the application.

This demo uses a simple Node.js application to feed the MQTT broker with random messages (at fixed interval of 500 ms), which can be displayed on the subscription panel once the related subscription is made.

Overall Architecture

Here the overall architecture of the demo:


If you want to install a version of this demo pointing to your local MQTT.Cool, follows these steps.

  • As prerequisite, this demo needs an up and running MQTT broker. You can choose whatever MQTT broker you prefer, or may also use one of the available public broker (an up-to-date list is maintained at

  • Download and configure an MQTT.Cool instance. Please refer to web site download page to find the MQTT.Cool package. MQTT.Cool comes with a set of predefined configurations for connecting with local MQTT server instances, as well as with the most common publicly accessible brokers. If you want to provide a new custom configuration, open the brokers_configuration.xml file located under <MQTT.COOL_HOME>/conf and provide a set of entries similar to the following (please refer to the inline documentation for more in-depth information on how to configure broker connection parameters):

    <!-- MQTT broker connection parameters for a local instance
         listening on port 1883, aliased by "mybroker". -->
    <param name="mybroker.server_address">tcp://localhost:1883</param>
    <param name="mybroker.connection_timeout">5</param>
    <param name="mybroker.keep_alive">20</param>
    • Get the file from the releases of this project, unzip it and copy the demo-auth-hooks-2.0.0.jar from lib into <MQTT.COOL_HOME>/hook/lib.

    • As the project contains two different Hook implementations, cool.mqtt.examples.auth_hooks.AuthHook and cool.mqtt.examples.auth_hooks.AuthHookWithAuthCache, edit the brokers_configuration.xml file by adding the class name of the Hook you are going to use, in the <hook_class> tag, just before <configuration>:

      • for the direct version:
      • for the cached version:
  • Launch the MQTT.Cool server.

  • Download this project.

  • As the latest version of the MQTT.Cool JavaScript library is always available through unpkg, it is hot-linked in the html page.

  • jQuery is currently hot-linked in the html page: you may want to replace it with a local version and/or to upgrade its version.

  • Deploy this demo on MQTT.Cool (used as Web server) or in any external Web server. If you choose the former, create a folder with name such as AuthDemo under the <MQTT.COOL_HOME>/pages folder, and copy there the contents of src/web of this project.

  • If required, install Node.js

  • From the src/feed folder, locally install the feed application:

npm install


To build your own version of demo-auth-hooks-2.0.0.jar, instead of using the one provided in the file from the Install section above, follow these steps:

  • Assuming that maven is installed on your machine, build the Hook by executing the package goal:
$ mvn package
  • Locate the jar file (which should be in the target folder) and drop it into <MQTT.COOL_HOME>/lib.


The demo assumes that the MQTT.Cool server is launched from localhost, but if you need to target a different server, search in src/web/js/app/Main.js this line:

MQTT_COOL_URL: 'http://localhost:8080',

and change it accordingly.

Further, the demo will look for the mosquitto alias, which is one of the predefined configurations in brokers_configuration.xml. Once more, if you need to target a different MQTT broker, and provided that relative connection parameters are already defined as shown above, modify the following line in src/web/js/app/Main.js:

mqttClient = mqttCoolSession.createClient('mosquitto');

and change it by replacing mosquitto with the new alias that maps the MQTT broker you are going to use.


Open your browser and point it to http://localhost:8080/AuthDemo, or to the address according to the host and/or the name of the folder where you deployed the project.

From the feed folder, run the feed application to publish random messages:

npm start <url_broker>

where url_broker is the url of the MQTT broker relative to the alias in use.

See Also

MQTT.Cool Compatibility Notes

  • Compatible with MQTT.Cool SDK for Web Clients version 1.0.0 or newer.
  • Compatible with MQTT.Cool SDK for Java Hooks version 1.1.0 or newer.
  • Compatible with MQTT.Cool since version 2.0.0 or newer.