Question:
I wonder if there is any solution for authentication vb.net webclient to download a file with login and password site that uses cookies.
The solution is that the HTTP request sent by your app must include the cookies required for authentication. To do so requires that you know the cookie names and values to be sent. Your app would need to add the cookies to the HTTP request header as shown here: http://www.example-code.com/vbnet/http_addCookies.asp