I see that there is websocket endpoint which works out fins with Java tests. In logs I see
Connecting to: ws://127.0.0.1:8080/76f48a44-0af8-444c-ba97-3f1ed34af
I wrote a cURL like WebSocket client. You can send single data frame (text/binary) via this tool and then it closes the socket. Also you can add HTTP headers in the initial HTTP upgrade process.
https://github.com/jussmen/WebSocket_cURL