Запросить windows авторизацию

Для отображения диалогового окна можно использовать функцию CredUIPromptForWindowsCredentials, а для проверки логина и пароля - PrincipalContext (добавить ссылку на System.DirectoryServices.AccountManagement).

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.DirectoryServices.AccountManagement;
using System.Text;
using System.Runtime.InteropServices;
using System.Windows.Forms;
namespace WinformsTest
{
    public partial class Form1 : Form
    {
        //https://www.pinvoke.net/default.aspx/credui.creduipromptforwindowscredentials
        [DllImport("credui.dll", CharSet = CharSet.Unicode)]
        private static extern uint CredUIPromptForWindowsCredentials(ref CREDUI_INFO notUsedHere,
          int authError,
          ref uint authPackage,
          IntPtr InAuthBuffer,
          uint InAuthBufferSize,
          out IntPtr refOutAuthBuffer,
          out uint refOutAuthBufferSize,
          ref bool fSave,
          uint flags);
        [DllImport("credui.dll", CharSet = CharSet.Auto)]
        private static extern bool CredUnPackAuthenticationBuffer(int dwFlags, IntPtr pAuthBuffer, uint cbAuthBuffer, 
            StringBuilder pszUserName, ref int pcchMaxUserName, StringBuilder pszDomainName, 
            ref int pcchMaxDomainame, StringBuilder pszPassword, ref int pcchMaxPassword
            );
        [DllImport("ole32.dll")]
        public static extern void CoTaskMemFree(IntPtr ptr);
        public Form1()
        {
            InitializeComponent();
        }
        bool CheckCredentials()
        {
            bool save = false;
            int errorcode = 0;
            uint dialogReturn;
            uint authPackage = 0;
            IntPtr outCredBuffer;
            uint outCredSize;
            CREDUI_INFO credui = new CREDUI_INFO();
            credui.cbSize = Marshal.SizeOf(credui);
            credui.pszCaptionText = "Авторизация";
            credui.pszMessageText = "Введите логин и пароль";
            credui.hwndParent = this.Handle;
            //Show dialog
            dialogReturn = CredUIPromptForWindowsCredentials(ref credui,
            errorcode, ref authPackage, (IntPtr)0, 0, out outCredBuffer, out outCredSize, ref save,
            0x1 /*CREDUIWIN_GENERIC*/);
            if (dialogReturn != 0) return false; //Cancel pressed
            var usernameBuf = new StringBuilder(100);
            var passwordBuf = new StringBuilder(100);
            var domainBuf = new StringBuilder(100);
            int maxUserName = 100;
            int maxDomain = 100;
            int maxPassword = 100;
            //Validate credentials
            if (CredUnPackAuthenticationBuffer(0, outCredBuffer, outCredSize, usernameBuf,
                ref maxUserName, domainBuf, ref maxDomain, passwordBuf, ref maxPassword))
            {
                CoTaskMemFree(outCredBuffer);
                using (PrincipalContext context = new PrincipalContext(ContextType.Machine)) 
                {
                    bool valid;
                    try
                    {
                        valid = context.ValidateCredentials(usernameBuf.ToString(), passwordBuf.ToString());
                    }
                    catch (System.DirectoryServices.AccountManagement.PrincipalOperationException ex)
                    {
                        MessageBox.Show(ex.ToString(), "Ошибка");
                        valid = false;
                    }
                    return valid;
                }
            }
            else throw new ApplicationException("CredUnPackAuthenticationBuffer failed");
        }
        private void button1_Click(object sender, EventArgs e)
        {
            if (!CheckCredentials()) MessageBox.Show("Не удалось авторизоваться");                        
        }
    }
    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    public struct CREDUI_INFO
    {
        public int cbSize;
        public IntPtr hwndParent;
        public string pszMessageText;
        public string pszCaptionText;
        public IntPtr hbmBanner;
    }

}