Passing credentials from asp net SharePoint?

 hi, i have a asp.net site with auteticacion form, and to use a document management sharepoint auteticacion digest, the problem I have is that users have to authenticate twice.
my question is if I can emulate a Windows authentication and send it to sharepoint to not ask for authentication.
I found an example, but say that does not work with response.redirect
 
Dim query As String = "http://somehost/default.aspx"
Dim request As WebRequest = HttpWebRequest.Create(query)
Dim cc As CredentialCache = New CredentialCache()
request.Credentials = New NetworkCredential("test2", "test2")
Dim response As HttpWebResponse = request.GetResponse()
Dim r As StreamReader = New StreamReader(response.GetResponseStream(), Encoding.ASCII)
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