5-improve-encrypted-storage (#6)

Added the use of DEK's for encryption of secrets. Both the KEK's and DEK's are stored in a way that you can have multiple key of which one is active. But the others are still available for decrypting. This allows for implementing key rotation.

Co-authored-by: eelke <eelke@eelkeklein.nl>
Co-authored-by: Eelke76 <31384324+Eelke76@users.noreply.github.com>
Reviewed-on: #6

IdentityShroud.Core/Model/RealmKey.cs

@@ -0,0 +1,27 @@
+using System.ComponentModel.DataAnnotations.Schema;
+using IdentityShroud.Core.Contracts;
+using IdentityShroud.Core.Security;
+using Microsoft.EntityFrameworkCore;
+
+namespace IdentityShroud.Core.Model;
+
+
+[Table("realm_key")]
+public record RealmKey
+{
+    public required Guid Id { get; init; }
+    public required string KeyType { get; init; }
+
+    
+    public required EncryptedDek Key { get; init; }
+    public required DateTime CreatedAt { get; init; }
+    public DateTime? RevokedAt { get; set; }
+
+    /// <summary>
+    /// Key with highest priority will be used. While there is not really a use case for this I know some users
+    /// are more comfortable replacing keys by using priority then directly deactivating the old key.
+    /// </summary>
+    public int Priority { get; set; } = 10;
+    
+
+}