Proxy to backend for WebSocket

It's perfectly working for Http, but not for WebSocket. I did not find the documentation about this. How can I do proxy for WS?
ng serve --proxy-config proxy.conf.json
proxy.conf.json:

{
  "/": {
    "target": "http://localhost:8080",
    "secure": false
  }
}

{
  "/": {
    "target": "http://localhost:8080",
    "secure": false
    "ws":true
  }
}

[lidebug]

{
  "/ws": {
    "target": "ws://localhost:8000",
    "secure": false,
    "ws": true
  }
}

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