Add a function to the OK button

Imports System.Runtime.InteropServices
Imports System.Text
Imports System.Net

Public Class Form1
    <DllImport("ole32.dll")> _
    Public Shared Sub CoTaskMemFree(ByVal ptr As IntPtr)
    End Sub

    <StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Auto)> _
    Private Structure CREDUI_INFO
        Public cbSize As Integer
        Public hwndParent As IntPtr
        Public pszMessageText As String
        Public pszCaptionText As String
        Public hbmBanner As IntPtr
    End Structure

    <DllImport("credui.dll", CharSet:=CharSet.Auto)> _
    Private Shared Function CredUnPackAuthenticationBuffer(ByVal dwFlags As Integer, ByVal pAuthBuffer As IntPtr, ByVal cbAuthBuffer As UInteger, ByVal pszUserName As StringBuilder, ByRef pcchMaxUserName As Integer, ByVal pszDomainName As StringBuilder, _
 ByRef pcchMaxDomainame As Integer, ByVal pszPassword As StringBuilder, ByRef pcchMaxPassword As Integer) As Boolean
    End Function

    <DllImport("credui.dll", CharSet:=CharSet.Auto)> _
    Private Shared Function CredUIPromptForWindowsCredentials(ByRef notUsedHere As CREDUI_INFO, ByVal authError As Integer, ByRef authPackage As UInteger, ByVal InAuthBuffer As IntPtr, ByVal InAuthBufferSize As UInteger, ByRef refOutAuthBuffer As IntPtr, _
 ByRef refOutAuthBufferSize As UInteger, ByRef fSave As Boolean, ByVal flags As Integer) As Integer
    End Function

    Public Shared Sub GetCredentials(ByRef networkCredential As NetworkCredential)
        Dim credui As New CREDUI_INFO()
        credui.pszCaptionText = String.Empty
        credui.pszMessageText = "The server 10.28.160.20 at NSW Department of Education and Training requires a username and password" + Environment.NewLine + Environment.NewLine +
            "Warning: This server is requesting that your username and password be sent in an insecure manner (basic authentication without a secure connection)."
        credui.cbSize = Marshal.SizeOf(credui)
        Dim authPackage As UInteger = 0
        Dim outCredBuffer As New IntPtr()
        Dim outCredSize As UInteger
        Dim save As Boolean = False
        ' Generic 
        Dim result As Integer = CredUIPromptForWindowsCredentials(credui, 0, authPackage, IntPtr.Zero, 0, outCredBuffer, _
         outCredSize, save, 1)

        Dim usernameBuf = New StringBuilder(100)
        Dim passwordBuf = New StringBuilder(100)
        Dim domainBuf = New StringBuilder(100)

        Dim maxUserName As Integer = 100
        Dim maxDomain As Integer = 100
        Dim maxPassword As Integer = 100
        If result = 0 Then
            If CredUnPackAuthenticationBuffer(0, outCredBuffer, outCredSize, usernameBuf, maxUserName, domainBuf, _
             maxDomain, passwordBuf, maxPassword) Then
                CoTaskMemFree(outCredBuffer)
                networkCredential = New NetworkCredential() With { _
                 .UserName = usernameBuf.ToString(), _
                 .Password = passwordBuf.ToString(), _
                 .Domain = domainBuf.ToString() _
                }
                Return
            End If
        End If

        networkCredential = Nothing
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim nc As New NetworkCredential()
        GetCredentials(nc)
        If nc IsNot Nothing Then 'We need to check if the credentials are there or not
            Dim username As String = nc.UserName 'This is the username
            Dim password As String = nc.Password 'This is the password
        End If
    End Sub
End Class