Bad signature for documents shared between users with userkey encryption.

Describe the bug
Collabora Online is not working well for documents shared between users with server configured with userkey encryption.

To Reproduce
Steps to reproduce the behavior:

1. Create a Collabora Document (like an .odt)
2. Share it with an other user
3. Both users modify the document
4. Close and reopen document (sometimes it works, sometimes not)
5. Having different errors :
   5.a) In front-end This application requires Javascript... Bad Signature
   
   5.b) In Firefox logs, some errors - not sure they are related Please do NOT wait for the DOMContentLoaded before registering your viewer handler or Content Security Policy: Les paramètres de la page ont empêché le chargement d’une ressource à eval (« script-src »).
   5.c) Docker logs

kit-01676-00034 2021-12-27 15:12:39.616180 +0000 [ kitbroker_070 ] ERR  Child session [608] not found to forward message: disconnect| kit/Kit.cpp:1482
wsd-00001-01692 2021-12-27 15:12:56.197008 +0000 [ docbroker_070 ] WRN  Waking up dead poll thread [HttpSynReqPoll], started: false, finished: false| ./net/Socket.hpp:718

Client details:

• OS: Linux
• Browser : Firefox 95 and Chromium

Server details

Operating system: Ubuntu 20.04

Web server: Nginx

Database: MariaDB

PHP version: 8.0

Nextcloud version: 23.0

Version of the richdocuments app 5.0.1

Version of Collabora Online 21.11.6

I have the same issue with Docker Collabora, CODE Integrated Server or Demo Server

I'm not sure if I have to write the issue here or on Collabora repo.

Thanks for your help :)

Start with the reproduction steps for shared documents under userkey encryption and compare the successful and failing reopen cases. Review the reported “Bad Signature” and Docker log messages first; done means both users can modify, close, and reopen a shared document without signature errors.