When you enabled anonymous access you must specified with which user anonymous users will connect. For this you can use a specific one or just the identity of the application pool.
The difference is simplified the user. Every application pool is running under an identity (user).
From my understanding you have two options.
a) Just create a virtual directory, point it to the SWD folder. Enable anonymous access, IUSR is fine or create a specific one. Make sure that this one has the right to access the directory.
Under this curcumstances everyone will allowed to access the swd depot. (not recommended if you ask me) and you can not validate against preferred server as you are setting username and password here.
b) Just create a virtual directory, point it to the SWD folder. Set access to Windows Authentication. Make sure that the user/password under the preferred server has rigths to access the directory.
Enable directory browsing on the virtual directory. (This should do the trick) and you can validate the credentials over preferred server.
Hope this helps
Thank you Juan, I really appreciate your help.