In the case of an aggressive WebDAV client, which opens hundreds of sessions pro minutes, the WebDAV implements create and store in the session the resource root, the list of all folders the user can see. If the user can access 1'000 courses, this leads to a high memory consumption despite the short session time to live.
A simple solution is to cache and share the resource root across the sessions. The resource root is only lists of folders, it is stateless. It only has access and permissions informations which is user related.