How do validate username and password with .text file

public partial class MainWindow : Window
    {
        public static GestionnaireGuichet guichet = new GestionnaireGuichet();

        public MainWindow()
        {
            InitializeComponent();
        }

        int count = 0;
        private void button_Click(object sender, RoutedEventArgs e)
        {
            
            if (count == 3)
            {
                this.Close();
            }
            if ((string.IsNullOrEmpty(user.Text)) || (string.IsNullOrEmpty(pass.Password)))
            {
                MessageBox.Show("Provide a valide username and password");
            }
            if ((user.Text.Length > 0) || (pass.Password.Length > 0))
            

            { 
                OperationCompte operation = new OperationCompte();
                this.Close();
                operation.Show();

            }
            else
                count++;
        
        }

public bool ValidatePassword(string username, string password)
        {
            string[] strArray = System.IO.File.ReadAllLines(@"D:\Project\Guichet\Guichet\bin\Debug\client.txt");

            if (username != strArray[0]) return false; //Wrong username

            if (password != strArray[1]) return false; //Wrong password

            if (username == strArray[0] && password == strArray[1]) return true; //good validation




            else
                return false;

        }

public bool LireClient()
       {
           string[] strArray;
           StreamReader sr = new StreamReader("client.txt");
           string strLine = sr.ReadLine();
           while (strLine != null)
           {
               strArray = strLine.Split(',');
               client.Add(new Client(strArray[0], strArray[1]));
               strLine = sr.ReadLine();
           }
           sr.Close();
           return true;

       }