Add project files.

formLogin.xaml.cs

@@ -0,0 +1,59 @@
+using System.Windows;
+using System;
+using Npgsql;
+
+namespace SportsTrainingApp
+{
+
+    public partial class formLogin : Window
+    {
+        formMain formMain;
+        public formLogin(formMain _formMain)
+        {                                                                                                                               
+            InitializeComponent();
+            formMain = _formMain;
+        }
+
+        private void Button_Click_2(object sender, RoutedEventArgs e)
+        {
+            this.Close();
+        }
+
+        private void Button_Click_1(object sender, RoutedEventArgs e)
+        {
+            int user_id = CheckUser(loginBox.Text, passwordBox.Password);
+            if (user_id != -1)
+            {
+                new formActivity(user_id).Show();
+                this.Close();
+                formMain.Close();               
+            }
+            else
+                MessageBox.Show("Неверный логин/пароль!");
+        }
+
+        public static int CheckUser(string username, string password)
+        {
+            using (var conn = new NpgsqlConnection(formMain.connectionString))
+            {
+                conn.Open();
+
+                using (var cmd = new NpgsqlCommand("SELECT id FROM dbo.users WHERE username = @username " +
+                    "AND password_hash = dbo.crypt(@password, password_hash)", conn))
+                {
+                    cmd.Parameters.AddWithValue("username", username);
+                    cmd.Parameters.AddWithValue("password", password);
+
+                    using (var reader = cmd.ExecuteReader())
+                    {
+                        if (reader.Read())
+                        {
+                            return reader.GetInt32(0);
+                        }
+                    }
+                    return -1;
+                }
+            }
+        }
+    }
+}