Remote Document Retrieval From Http

I have been doing some research to determine an efficient and secure way to pass a document located on another server in the network to our web server and then on to the intranet user that requested it. While I have found plenty of ways to do this, I am not that experienced with this scenario as I have always just served documents stored locally on the web server and located nowhere else.

Our document server is shared in the domain and everyone has access to it and depending on their permissions, can access many files. I was thinking that I could possibly grab a file if I could pass the intranet users credentials but I don't know where to look to do that.

I was also thinking that maybe a webservice could do what I need but that just doesn't seem right to me because I am kinda guessing that there is already a .net library available that already handles something like this but am unsure as to what it is.