Rudder

In https://github.com/Normation/rudder/pull/5229 I changed the way that CurrentUser was computed and stored in session because it lead to error in several page.

At the time, I supposed it was due to the session fixation prevention process built in spring security, and that lift was trying to use the old (destroyed) session in place of the new one in some context.
That first correction helped, but we still have a problem: in the context of async requests (at least when using lazy-load which uses under the hood AsyncRenderComet.asyncRender), SecurityContextHolder is lost.

I suppose it have to do with the way the session snapshot is done, and perhaps of a similar cause than previously (session moved in the async context?)