User Sign-in and License Validation in Office Online Server (WOPI)

Question

We have a product which is successfully integrated with Office for the web (Office Online Server) through Web Application Open Platform Interface (WOPI) since long time ago.

In the past before 2023, we noticed that user needs to sign-in to Office365 before opening the Office Online editing mode through WOPI. However, now it seems user does not longer need to sign-in to Office365 anymore to open the Office Online editing mode through WOPI. Without being signed-in to Office365, user can edit the document in Office Online Server.

This new behavior introduces some questions for enterprises related to security aspects, especially related to which license is being used or which account is owned this document. Hence, we have been exploring the archived documentation to find out the differentiation compared to the new documentation. Finally we found the information from the internet as described below.

• Archived documentation https://web.archive.org/web/20200924150317/https://wopi.readthedocs.io/en/latest/scenarios/business.html.
• New documentation https://learn.microsoft.com/en-us/microsoft-365/cloud-storage-partner-program/online/scenarios/business

Based on the above finding, we found that there is a section which was found in the archived documentation but it seems missing in the new documentation, as shown below, and it might be related to the user sign-in validation or license validation.

Questions :

1. Is there any changes in the flow related to user sign-in validation or license validation when opening Office Online editing mode through WOPI, so that the user can open/edit the document without being signed-in to Office365?
2. When opening Office Online editing mode, which account in Office365 or license is being used for editing the document in Office Online?
3. Where is the document stored during the editing mode and belongs to which account in Office365?

Thank you