Websocket server

Hello, I want to make a websocket server, it works with the basic settings, but I need to use modifyHandshake(....) method in the ServerEndpointConfig.Configurator class. The modifyHandshake was called when the client tried to connect, but the client don't get the responseheaders. Is there anyone who made it work, or have an idea what should I try? I use this Core.addWebSocketEndpoint(String path, Endpoint endpoint), based on this docs: https://docs.mendix.com/refguide/websockets-in-runtime/ Mendix uses websocket internally so I think maybe I have to use this (picture https://abhishek-gupta.gitbook.io/java-websocket-api-handboo...) instead of the @ServerEnpdoint annotation, but I couldn't get it to work.   Thanks in Advance!
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