How do I implement custom messages, just like websockets

I have a requirement that the client only sends data to the server, and the server can freely choose who to push messages to, just like a native websocket. The purpose of doing so is to send authentication information to the server, and the server can return the permissions I have, such as read-only. I know this can be achieved using websocket, but I hope to directly access agent.custom during the authentication process and bind the permission information to it.

Start by reviewing the authentication process and the references to agent.custom in the issue, then compare the requested behavior with native websocket message routing. Confirm whether the project has an existing entry point for server-directed custom messages and permission data; the issue is complete only when the intended behavior and its scope are clearly defined.