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

Server Dashboard/ViewModels/Interfaces/IHavePassword.cs

@@ -0,0 +1,10 @@
+using System;
+using System.Collections.Generic;
+using System.Security;
+using System.Text;
+
+namespace Server_Dashboard {
+    public interface IHavePassword {
+        SecureString SecurePassword { get; }
+    }
+}