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STATUS_FORMS_AUTH_REQUIRED
The file-style request reached a server gated by forms authentication
STATUS_FORMS_AUTH_REQUIRED is about authentication workflow, not local file permissions. The status text instructs the user to browse to the site and sign in. Microsoft's Office Forms Based Authentication Protocol formalizes this pattern for HTTP-based Office clients when Windows or other authentication mechanisms are not available.
In MS-OFBA discovery, a server can return an X-FORMS_BASED_AUTH_REQUIRED header containing the login-page URI. The client must navigate to that page to establish identity, then use the resulting authenticated state for the document request. A filesystem-style WebDAV or Office operation that lacks the browser/session state can therefore receive this status even when the user's account is valid.
Do not solve the problem by granting Everyone access to the document library. Capture the HTTP authentication discovery response, login URI, cookies or tokens managed by the supported client, and the identity used after sign-in.
What to inspect
- The HTTP response headers, especially the forms-authentication required and return URLs.
- Whether the client supports MS-OFBA or another server-supported interactive authentication flow.
- Session expiration, cookie/token persistence and differences between browser and WebDAV/Office access.
References
- Microsoft Open Specifications: MS-OFBA
- Microsoft Open Specifications: Forms Based Authentication Required header
- Microsoft: Using the WebDAV Redirector
- Microsoft Open Specifications: NTSTATUS values
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