There is a very long thread on the TechNet forums regarding an unusual authentication issue when DirectAccess clients try to connect to SharePoint sites. There were a lot of posts and a lot of effort was made to determine the nature of the problem. The good news I have for you today is that we’ve solved the problem and have published a fix!
The problem was due to the fact that the automatic logon level for Windows HTTP Services (WinHTTP) is Medium. When the automatic logon level is set to Medium, it prevents the user credentials from being automatically sent to the web server. The end result is that the address is considered an Internet server when you try to access the WebDAV resource like SharePoint which leads to you being asked for credentials.
Here’s the fix for the problem:
Microsoft DAIP iX/SCD iX
UAG Direct Access/Anywhere Access Group (AAG)
The “Edge Man” blog (DA all the time): http://blogs.technet.com/tomshinder/default.aspx
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