MVC ASP.NET Return response.GetResponseStream() as FileResultStream
public FileResult SomeAction()
{
    var request = Make some request here

    using (var response = (HttpWebResponse)request.GetResponse())
    {
        string contentType = response.ContentType;
        return File(response.GetResponseStream(),contentType);
    }
}

var response = request.GetResponse();
File(response.GetResponseStream(), response.ContentType);