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/Security/KekId.cs

@@ -0,0 +1,41 @@
+using System.ComponentModel;
+using System.Globalization;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace IdentityShroud.Core.Security;
+
+[JsonConverter(typeof(KekIdJsonConverter))]
+[TypeConverter(typeof(KekIdTypeConverter))]
+public readonly record struct KekId
+{
+    public Guid Id { get; } 
+
+    public KekId(Guid id)
+    {
+        Id = id;
+    }
+
+    public static KekId NewId()
+    {
+        return new KekId(Guid.NewGuid());
+    }
+}
+
+public class KekIdJsonConverter : JsonConverter<KekId>
+{
+    public override KekId Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        => new KekId(reader.GetGuid());
+
+    public override void Write(Utf8JsonWriter writer, KekId value, JsonSerializerOptions options)
+        => writer.WriteStringValue(value.Id);
+}
+
+public class KekIdTypeConverter : TypeConverter
+{
+    public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
+        => sourceType == typeof(string) || base.CanConvertFrom(context, sourceType);
+
+    public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
+        => value is string s ? new KekId(Guid.Parse(s)) : base.ConvertFrom(context, culture, value);
+}