Connection to MQTT server over WebSocket fails from web browser

[epieffe]

Describe the bug
Connection to Zilla MQTT server over WebSocket fails from web browser.

The same javascript code executed on nodejs, outside a web browser, connects successfully.

To Reproduce
To quickly reproduce the issue I created a GitHub repo with a compose.yaml file that starts Zilla with Kafka and a simple index.html page that uses MQTT.js to connect to the MQTT server. All the steps to reproduce the problem are described in the README:

https://github.com/epieffe/zilla-mqtt-ws-test

In short:

1. Start Zilla with MQTT and WebSocket bindings
2. Connect to the MQTT server from a web browser
3. The connection fails

Expected behavior
The web browser successfully connects to Zilla MQTT server.

Additional context
I ran the same index.html with the EMQX MQTT broker and it successfully connects, both on Firefox and Google Chrome.

[ankitk-me]

We have identified the issue with the config, please update http_server with mentioned change:

options:
      access-control:
        policy: cross-origin

After the update, http_server should look like:

http_server:
    type: http
    kind: server
    options:
      access-control:
        policy: cross-origin
    routes:
      - when:
          - headers:
              :scheme: http
              upgrade: websocket
          - headers:
              :scheme: https
              upgrade: websocket
        exit: ws_server

Screenshot for validation: