Why Office Asks for Proxy Login After the Browser Already Signed In
A browser-authenticated request does not authenticate a separate legacy Word, Excel or PowerPoint connection.
Opening a document in desktop Office can start another network client. Identify the process owning the prompt and the response triggering it before reusing browser credentials.
| Evidence | Recipient |
|---|---|
| 407 / Proxy-Authenticate | Intermediary |
| 401 / WWW-Authenticate | Document server |
| Application sign-in | Its own authentication flow |
SecureLogin's documented Office 2003 case identified WINWORD.EXE/POWERPNT.EXE separately from IEXPLORE.EXE. Compare the actual Office route and supported scheme with the browser. Client-identifier policy can differ too, as Microsoft documented for Office 2016 for Mac 16.9 onward.
If only a local copy is needed, downloading in the browser changes which client retrieves it. Editing and saving back still needs the desktop application's own supported network workflow.