added user password hashing

src/QuickDish.Core/User.cs

@@ -12,4 +12,20 @@ internal class User
     public string Username { get; set; }
     public string PasswordHash { get; set; }
 
+    public User(int id, string username, string passwordHash)
+    {
+        if (id <= 0)
+            throw new ArgumentOutOfRangeException("User Id must be positiv", nameof(id));
+
+        if (string.IsNullOrWhiteSpace(username))
+            throw new ArgumentException("Username can't be empty", nameof(username));
+
+        if (string.IsNullOrWhiteSpace(passwordHash))
+            throw new ArgumentException("Password hash can't be empty", nameof(passwordHash));
+
+        Id = id;
+        Username = username;
+        PasswordHash = passwordHash;
+    }
+
 }