C# Definition:

[ComImport]
[Guid("79EAC9D0-BAF9-11CE-8C82-00AA004BA90B")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
interface IAuthenticate {
   [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
   void Authenticate(IntPtr phwnd,
    [MarshalAs(UnmanagedType.LPWStr)] ref string pszUsername,
    [MarshalAs(UnmanagedType.LPWStr)] ref string pszPassword);
}

VB Definition:

<ComImport> _
<Guid("79EAC9D0-BAF9-11CE-8C82-00AA004BA90B")> _
<InterfaceType(ComInterfaceType.InterfaceIsIUnknown)>
Interface IAuthenticate
   <MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)>
   Sub Authenticate(IntPtr phwnd,
    <MarshalAs(UnmanagedType.LPWStr)> ByRef string pszUsername,
    <MarshalAs(UnmanagedType.LPWStr)> ByRef string pszPassword)
End Interface

User-Defined Types:

None.

Notes:

    Example:
    [ClassInterface(ClassInterfaceType.None)]
    public class Downloader : IBindStatusCallback, IDisposable, IAuthenticate
    {
    public void Download()
    {
    URLDownloadToFile(IntPtr.Zero, SourcePath , LocalPath ,0,(IBindStatusCallback)this);
    }
    /// <summary>
    /// Authenticates the specified user.
    /// </summary>
    /// <param name="phwnd">The HWND of the parent window for a default user interface.</param>
    /// <param name="pszUsername">The username to use for authentication.
    ///Client should also set phwnd to zero.</param>
    /// <param name="pszPassword">The password.</param>
    public void Authenticate(IntPtr phwnd, ref string pszUsername, ref string pszPassword)
    {
        // Downloader.Authenticate implementation
        phwnd = IntPtr.Zero;
        pszUsername = "ProxyUserName";
        pszPassword = "ProxyPassword";
    }
    }