Vaadin 8.8.0 and Jetty 9.4 incompatibility

Vaadin Framework version : 8.8.0
embedded Jetty Version: 9.4.18.v20190429
I also set up: (manually enforce use of Jetty93AsyncSupportWithWebSocket)

ApplicationConfig.PROPERTY_SESSION_SUPPORT = true
ApplicationConfig.PROPERTY_ALLOW_SESSION_TIMEOUT_REMOVAL =true
ApplicationConfig.PROPERTY_COMET_SUPPORT,
= org.atmosphere.container.Jetty93AsyncSupportWithWebSocket"

• Actual behavior
  Right after loading a page, with WebSocket switched up, Vaadin server responds with Session Expired. No delays, the first push with the protocol upgrade to websocket immediatly has the Session Timout error message.

• Expected behavior
  Continue push operations using Websocket

Minimal reproducible example:
a repo that reproduces the problem: https://github.com/padisah/vaadin-jetty94-failure/

Reason of problem:
Jetty 9.3 -> 9.4 version change had a breaking change. They started treating Websocket session NOT as an HttpSession but a different session implementation for websockets. This new implementation doesn't provide JSESSIONID anymore.

Atmosphere has suffered from that change, so they had a fix over that, but Vaadin still tries to look up the HttpSession from the websocket upgraded connection's request.

PushHandler.class line 205
`
private void callWithUi(final AtmosphereResource resource,
final PushEventCallback callback, boolean websocket) {
AtmosphereRequest req = resource.getRequest();
VaadinServletRequest vaadinRequest = new VaadinServletRequest(req,
service);
VaadinSession session = null;
if (websocket) {
// For any HTTP request we have already started the request in the
// servlet
service.requestStart(vaadinRequest, null);
}
try {
try {
session = service.findVaadinSession(vaadinRequest); // here pushandler starts looking up an HttpSession

`
above call continues to:

line 949, VaadinService.getWrappedSession

Switching to JSR356AsyncSupport instead starts the application, but the log is constantly filled with error messages realted to failed push operations, and it actually fails with a higher load when multiple browsers need to get pushes frequently. I would rather use a jetty-specific websocket implementation.

references:
https://vaadin.com/forum/thread/17053341/session-immediately-expires-after-upgrade-jetty-server-to-9-4-6

https://github.com/Atmosphere/atmosphere/issues/2241

Start with the minimal reproducer and inspect PushHandler.java around line 205, where the websocket path calls service.findVaadinSession. Then trace VaadinService.getWrappedSession around line 949 and review the linked Atmosphere issue for the Jetty 9.4 session behavior. Done means websocket push continues without an immediate Session Expired response under the reproducer.