MSOFBA stopped working with Version 2603 Build 16.0.19822.20086) 64 bits of microsoft word

Question

Subject: MSOFBA authentication cookie not persisting to WebDAV client after recent Office update

Hello,

I am a software developer working on an Electronic Document Management (EDM) solution that integrates with the Microsoft Office suite. Our integration relies on the WebDAV protocol for file access and uses MSOFBA to drive an OAuth 2.0 authentication flow against our identity provider.

This integration has been functioning correctly for some time, but following a recent Office update, the authentication flow is no longer completing successfully. Specifically:

• The OAuth 2.0 flow itself still completes as expected, and a valid access token is issued at the end of the browser-based sign-in.
• However, the authentication cookie that should be associated with the WebDAV session no longer appears to be set, and subsequent WebDAV requests are therefore unauthenticated.

My current hypothesis is that the MSOFBA dialog and the WebMini/WebClient process handling the WebDAV traffic are no longer sharing the same cookie container — i.e., the cookie may be correctly issued in the embedded authentication browser but is not propagated to the process that actually performs the WebDAV calls.

Affected versions (64-bit):

• Last known working version: Version 2112, Build 16.0.14729.20156
• First known broken version: Version 2603, Build 16.0.19822.20086

My questions for the community:

1. Has anyone observed similar behavior following a recent Office/Click-to-Run update?
2. Are there known changes to how MSOFBA shares session cookies with the WebClient service that third-party integrators should account for?
3. Are there recommended diagnostics (Fiddler traces, WebClient logs, registry keys) to confirm whether the cookie is being dropped between the authentication UI and the WebDAV client?

Any guidance or confirmation of similar issues would be greatly appreciated.

Thank you.