PhotoStudio_PM_04/LoginForm.cs

using System;
using System.Windows.Forms;
using Npgsql;

namespace PhotoStudioApp
{
    public partial class LoginForm : Form
    {
        private string connectionString = "Host=245e1-rw.db.pub.dbaas.postgrespro.ru;Port=5432;Database=dbproject;Username=smirnova_ul;Password=Q#Rto%g$$$5;SSL Mode=Require;Trust Server Certificate=true;";

        public LoginForm()
        {
            InitializeComponent();
        }

        private void btnLogin_Click(object sender, EventArgs e)
        {
            string login = txtLogin.Text;
            string password = txtPassword.Text;
            string hash = GetSHA256Hash(password);

            using (NpgsqlConnection conn = new NpgsqlConnection(connectionString))
            {
                conn.Open();
                string sql = "select u.user_id, r.role_name from users u join roles r on u.role_id = r.role_id where u.login = @login and u.password_hash = @hash";
                NpgsqlCommand cmd = new NpgsqlCommand(sql, conn);
                cmd.Parameters.AddWithValue("@login", login);
                cmd.Parameters.AddWithValue("@hash", hash);

                using (NpgsqlDataReader reader = cmd.ExecuteReader())
                {
                    if (reader.Read())
                    {
                        int userId = reader.GetInt32(0);
                        string role = reader.GetString(1);
                        MessageBox.Show($"Добро пожаловать, {login}! Роль: {role}");

                        MainForm mainForm = new MainForm(userId, role, login, connectionString);
                        mainForm.Show();
                        this.Hide();
                    }
                    else
                    {
                        MessageBox.Show("Неверный логин или пароль");
                    }
                }
            }
        }

        private string GetSHA256Hash(string input)
        {
            using (System.Security.Cryptography.SHA256 sha256 = System.Security.Cryptography.SHA256.Create())
            {
                byte[] inputBytes = System.Text.Encoding.UTF8.GetBytes(input);
                byte[] hashBytes = sha256.ComputeHash(inputBytes);
                return BitConverter.ToString(hashBytes).Replace("-", "").ToLower();
            }
        }

        protected override void OnFormClosing(FormClosingEventArgs e)
        {
            if (this.Owner == null)
            {
                Application.Exit();
            }
            base.OnFormClosing(e);
        }
    }
}