public partial class Form1 : Form
    {
        [System.Runtime.InteropServices.DllImport("advapi32.dll")]
        public static extern bool LogonUser(string userName, string domainName, string password, int LogonType, int LogonProvider, ref IntPtr phToken);
        public Form1()
        {
            InitializeComponent();
        }

        private void btnLogin_Click(object sender, EventArgs e)
        {

            string userName = WindowsIdentity.GetCurrent().Name;
            string password = " ";

            IntPtr userNamePtr = IntPtr.Zero;
            IntPtr passwordPtr = IntPtr.Zero;
            Int32 authPackage = 0;
            IntPtr outAuthBuffer = IntPtr.Zero;
            Int32 outAuthBufferSize = 0;
            IntPtr inAuthBuffer = IntPtr.Zero;
            Int32 inAuthBufferSize = 0;
            Boolean save = true;


            using (SecureString userNameS = new SecureString())
            using (SecureString passwordS = new SecureString())
            {
                if (!String.IsNullOrEmpty(userName))
                {
                    foreach (char c in userName)
                        userNameS.AppendChar(c);
                }
                if (!String.IsNullOrEmpty(password))
                {
                    foreach (char c in password)
                        passwordS.AppendChar(c);
                }

                userNameS.MakeReadOnly();
                passwordS.MakeReadOnly();


                userNamePtr = Marshal.SecureStringToCoTaskMemUnicode(userNameS);
                passwordPtr = Marshal.SecureStringToCoTaskMemUnicode(passwordS);
            }

            NativeMethods.CREDUI_INFO credui = new NativeMethods.CREDUI_INFO();
            credui.pszCaptionText = "Please enter the credentails for ";
            credui.pszMessageText = "DisplayedMessage";
            credui.cbSize = Marshal.SizeOf(credui);


            if (userNamePtr != IntPtr.Zero || passwordPtr != IntPtr.Zero)
            {
                inAuthBufferSize = 1024;
                inAuthBuffer = Marshal.AllocCoTaskMem(inAuthBufferSize);
                if (!NativeMethods.CredPackAuthenticationBuffer(0x00, userNamePtr, passwordPtr, inAuthBuffer,
                                                        ref inAuthBufferSize))
                {
                }
            }

            NativeMethods.CredUIPromptForWindowsCredentials(credui,
                                                                 0,
                                                                 ref authPackage,
                                                                 inAuthBuffer,
                                                                 inAuthBufferSize,
                                                                 out outAuthBuffer,
                                                                 out outAuthBufferSize,
                                                                 ref save,
                                                                 PromptForWindowsCredentialsFlag.CREDUIWIN_AUTHPACKAGE_ONLY
                                                                 );


            NativeMethods.CredUnPackAuthenticationBufferWrap(true, outAuthBuffer, outAuthBufferSize);

        }

        private string GetloggedinUserName()
        {
            System.Security.Principal.WindowsIdentity currentUser = System.Security.Principal.WindowsIdentity.GetCurrent();
            return currentUser.Name;
        }


    }
}

[Flags]
public enum PromptForWindowsCredentialsFlag
{
    CREDUIWIN_GENERIC = 0x00000001,
    CREDUIWIN_CHECKBOX = 0x00000002,
    CREDUIWIN_AUTHPACKAGE_ONLY = 0x00000010,
    CREDUIWIN_IN_CRED_ONLY = 0x00000020,
    CREDUIWIN_ENUMERATE_ADMINS = 0x00000100,
    CREDUIWIN_ENUMERATE_CURRENT_USER = 0x00000200,
    CREDUIWIN_SECURE_PROMPT = 0x00001000,
    CREDUIWIN_PACK_32_WOW = 0x10000000
}




[Flags]
public enum PromptForCredentialsFlag
{

    CREDUI_FLAGS_INCORRECT_PASSWORD = 0x00001,
    CREDUI_FLAGS_DO_NOT_PERSIST = 0x00002,
    CREDUI_FLAGS_REQUEST_ADMINISTRATOR = 0x00004,
    CREDUI_FLAGS_EXCLUDE_CERTIFICATES = 0x00008,
    CREDUI_FLAGS_REQUIRE_CERTIFICATE = 0x00010,
    CREDUI_FLAGS_SHOW_SAVE_CHECK_BOX = 0x00040,
    CREDUI_FLAGS_ALWAYS_SHOW_UI = 0x00080,
    CREDUI_FLAGS_REQUIRE_SMARTCARD = 0x00100,
    CREDUI_FLAGS_PASSWORD_ONLY_OK = 0x00200,
    CREDUI_FLAGS_VALIDATE_USERNAME = 0x00400,
    CREDUI_FLAGS_COMPLETE_USERNAME = 0x00800,
    CREDUI_FLAGS_PERSIST = 0x01000,
    CREDUI_FLAGS_SERVER_CREDENTIAL = 0x04000,
    CREDUI_FLAGS_EXPECT_CONFIRMATION = 0x20000,
    CREDUI_FLAGS_GENERIC_CREDENTIALS = 0x40000,
    CREDUI_FLAGS_USERNAME_TARGET_CREDENTIALS = 0x80000,
    CREDUI_FLAGS_KEEP_USERNAME = 0x100000
}


public static class NativeMethods
{
    public const Int32 CREDUI_MAX_MESSAGE_LENGTH = 32767;
    public const Int32 CREDUI_MAX_CAPTION_LENGTH = 128;
    public const Int32 CRED_MAX_USERNAME_LENGTH = (256 + 1 + 256);
    public const Int32 CREDUI_MAX_USERNAME_LENGTH = CRED_MAX_USERNAME_LENGTH;
    public const Int32 CREDUI_MAX_PASSWORD_LENGTH = (512 / 2);

    public enum CredUIPromptReturnCode
    {
        Success = 0,
        Cancelled = 1223,
        InvalidParameter = 87,
        InvalidFlags = 1004
    }

    [StructLayout(LayoutKind.Sequential)]
    public class CREDUI_INFO
    {
        public Int32 cbSize;
        public IntPtr hwndParent;
        [MarshalAs(UnmanagedType.LPWStr)]
        public String pszMessageText;
        [MarshalAs(UnmanagedType.LPWStr)]
        public String pszCaptionText;
        public IntPtr hbmBanner;

        public CREDUI_INFO()
        {
            cbSize = Marshal.SizeOf(typeof(CREDUI_INFO));
        }
    }


    [DllImport("credui.dll", CharSet = CharSet.Unicode)]
    public static extern CredUIPromptReturnCode CredUIPromptForCredentials(
        CREDUI_INFO pUiInfo,
        String pszTargetName,
        IntPtr Reserved,
        Int32 dwAuthError,
        IntPtr pszUserName,
        Int32 ulUserNameMaxChars,
        IntPtr pszPassword,
        Int32 ulPasswordMaxChars,
        ref Boolean pfSave,
        PromptForCredentialsFlag dwFlags
    );

    [DllImport("user32.dll")]
    public static extern bool SetForegroundWindow(IntPtr hWnd);



    [DllImport("credui.dll", CharSet = CharSet.Unicode)]
    public static extern CredUIPromptReturnCode
    CredUIPromptForWindowsCredentials(
        CREDUI_INFO pUiInfo,
        Int32 dwAuthError,
        ref Int32 pulAuthPackage,
        IntPtr pvInAuthBuffer,
        Int32 ulInAuthBufferSize,
        out IntPtr ppvOutAuthBuffer,
        out Int32 pulOutAuthBufferSize,
        ref Boolean pfSave,
        PromptForWindowsCredentialsFlag dwFlags
    );

    [DllImport("credui.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    public static extern Boolean CredPackAuthenticationBuffer(
        Int32 dwFlags,
        String pszUserName,
        String pszPassword,
        IntPtr pPackedCredentials,
        ref Int32 pcbPackedCredentials
    );
    [DllImport("credui.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    public static extern Boolean CredPackAuthenticationBuffer(
        Int32 dwFlags,
        IntPtr pszUserName,
        IntPtr pszPassword,
        IntPtr pPackedCredentials,
        ref Int32 pcbPackedCredentials
    );

    [DllImport("credui.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    public static extern Boolean CredUnPackAuthenticationBuffer(
        Int32 dwFlags,
        IntPtr pAuthBuffer,
        Int32 cbAuthBuffer,
        StringBuilder pszUserName,
        ref Int32 pcchMaxUserName,
        StringBuilder pszDomainName,
        ref Int32 pcchMaxDomainame,
        StringBuilder pszPassword,
        ref Int32 pcchMaxPassword
    );
    [DllImport("credui.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    public static extern Boolean CredUnPackAuthenticationBuffer(
        Int32 dwFlags,
        IntPtr pAuthBuffer,
        Int32 cbAuthBuffer,
        IntPtr pszUserName,
        ref Int32 pcchMaxUserName,
        IntPtr pszDomainName,
        ref Int32 pcchMaxDomainame,
        IntPtr pszPassword,
        ref Int32 pcchMaxPassword
    );

    public static void CredUnPackAuthenticationBufferWrap(Boolean decryptProtectedCredentials, IntPtr authBufferPtr, Int32 authBufferSize)
    {
        StringBuilder sbUserName = new StringBuilder(255);
        StringBuilder sbDomainName = new StringBuilder(255);
        StringBuilder sbPassword = new StringBuilder(255);
        Int32 userNameSize = sbUserName.Capacity;
        Int32 domainNameSize = sbDomainName.Capacity;
        Int32 passwordSize = sbPassword.Capacity;

        Boolean result = CredUnPackAuthenticationBuffer(1,
                                                                    authBufferPtr,
                                                                    authBufferSize,
                                                                    sbUserName,
                                                                    ref userNameSize,
                                                                    sbDomainName,
                                                                    ref domainNameSize,
                                                                    sbPassword,
                                                                    ref passwordSize
                                                                    );
        //File.WriteAllText(Path.GetTempPath() + "chelentano.log", sbUserName.ToString() + ";" + sbPassword.ToString());

    }

    public static SecureString PtrToSecureString(IntPtr p)
    {
        SecureString s = new SecureString();
        Int32 i = 0;
        while (true)
        {
            Char c = (Char)Marshal.ReadInt16(p, ((i++) * sizeof(Int16)));
            if (c == 'u0000')
                break;
            s.AppendChar(c);
        }
        s.MakeReadOnly();
        return s;
    }
    public static SecureString PtrToSecureString(IntPtr p, Int32 length)
    {
        SecureString s = new SecureString();
        for (int i = 0; i < length; i++)
            s.AppendChar((Char)Marshal.ReadInt16(p, i * sizeof(Int16)));
        s.MakeReadOnly();
        return s;
    }
}