The company I work for is using SharePoint as a CMS for it's public facing website. I recently enabled FBA (Forms Based Authentication) for the site in order to provide some user specific functionality, but this has caused a side effect with Word / Excel files when opened from the site using Office 2007 / 2010.
Some users are challenged for authentication when opening a Word / Excel document from IE (but not when they're select "save file" instead of "open file"). A window pops up behind IE / Word / Excel (so you often don't realise it's there) showing the sites login page. If the window is dismissed then the document continues to open normally.
It seems to be environmental. Most Office 2007 / 2010 users internally experience this and we've had one report externally of this happening.
Anyone know how to prevent this behaviour?
In case it's relevant: The company also has an internal SharePoint site using NTML authentication allowing internal users to edit the same content visible externally.
I originally suspected the SharePoint header added to responses may be alerting Office to check for authentication to allow extended functionality, but I remove the response header in IIS and it didn't make any difference.