See https://jira.spring.io/browse/INT-3888 and its PullRequest
Note: rework `StompIntegrationTests` logic to use SockJS Client (that was enabled on the server side before).
This helps us to use `sessionId` which is as a `user` key on subscription phase.
In case of Standard Tomcat WebSocket Client we end up with the race condition when both client and server uses the same
`static` variable in the `WsSession` class, so we can't determine the server session correctly by the id on the client side.
The subscribe/send/unsubscribe logic works well because we are based on the **web socket** for the session, independently of its id.
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