complete login function and login window also add attached properties and helper classes for securestring

Server Dashboard/Database/DatabaseHandler.cs

@@ -2,19 +2,37 @@
 using System;
 using System.Collections.Generic;
 using System.Configuration;
+using System.Data;
 using System.Data.SqlClient;
 using System.Reflection;
 
 namespace Server_Dashboard {
-    class DatabaseHandler {
+    public static class DatabaseHandler {
+
+        public static bool CheckLogin(string uname, string passwd) {
+            string valid = "False";
+            ConnectToDatabase(con => {
+                string query = "EXEC ValidateUserLogin @Username = @uname, @Password = @passwd, @Valid = @valid OUTPUT";
+                using (SqlCommand com = new SqlCommand(query, con)) {
+                    com.Parameters.AddWithValue("@uname", uname);
+                    com.Parameters.AddWithValue("@passwd", passwd);
+                    com.Parameters.Add("@valid", SqlDbType.NVarChar, 250);
+                    com.Parameters["@valid"].Direction = ParameterDirection.Output;
+                    com.ExecuteNonQuery();
+                    valid = Convert.ToString(com.Parameters["@Valid"].Value);
+                }
+            });
+            return Convert.ToBoolean(valid);
+        }
+
         #region Private methods
         /// <summary>
         /// Opens a database connection
         /// </summary>
         /// <param name="callback">Callback type SqlConnection</param>
         /// <returns></returns>
-        private SqlConnection ConnectToDatabase(Action<SqlConnection> callback) {
-            using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["Co2AuswertungDB"].ConnectionString)) {
+        private static SqlConnection ConnectToDatabase(Action<SqlConnection> callback) {
+            using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["ServerDashboardDB"].ConnectionString)) {
                 try {
                     con.Open();
                     callback(con);