http认证

        Dim MyUri As Uri = New Uri(txtURL.Text.Trim)

        Dim credCache As CredentialCache = New CredentialCache()
        credCache.Add(MyUri, "Negotiate", CredentialCache.DefaultNetworkCredentials)

        credCache.Add(MyUri, "Basic", New NetworkCredential("admin", "000000"))

        credCache.Add(MyUri, "Digest", New NetworkCredential("admin", "000000"))

        credCache.Add(MyUri, "Basic", New NetworkCredential("admin", "000000"))

        Dim req As HttpWebRequest = CType(WebRequest.Create(MyUri), HttpWebRequest)
        req.Credentials = credCache

        req.Method = "GET"
        'req.Credentials = New NetworkCredential(Me.UsernameTextBox.Text, Me.PasswordTextBox.Text)

        Using res As WebResponse = req.GetResponse, st As New System.IO.StreamReader(res.GetResponseStream, System.Text.Encoding.GetEncoding("EUC-jp"))
            Me.RichTextBox1.Text = ""
            Me.RichTextBox1.Text = st.ReadToEnd()
        End Using