I wrote here about a problem I had connecting to a Windows share that was using DFS from my Ubuntu 10.04 laptop. Turns out I was wrong about the issue being related to authentication.
The issue was that my server was sending back a string without the Windows file separator at the end (backslash "\"). I simply patched the code at the relevant place to check if the file separator was missing and put one in if needed. Not the most elegant patch, but probably less likely to impact any other code.
I'm being careful not to call this a bug in Samba. The file server was an EMC NAS implementation. Fairly common, but not a standard Windows server sharing files. Perhaps the EMC is out of spec on this point, or perhaps the spec is ambiguous on trailing file separators. Given the number of devices out there, I think it's reasonable to make the Samba client code handle the case, regardless of what the spec says.
I fed the patch to Ubuntu, because that's where I originally logged the issue. Building Samba was remarkably hassle free, as was getting the source from their git repository, thanks to good documentation for both. My thanks to the Samba team for a great product.