using System;

using System.Collections.Generic;

using System.Text.Json;

using System.Text.Json.Serialization;

public class Program

{

    public static void Main()

    {

        var extension = new DerivedExtensionA();

        extension.Properties.Add("SomeKey", "SomeValue");

        var allExtensions = new List<Extension>() { extension };

        string extensionSerialized =

                JsonSerializer.Serialize(

                    extension);

        Console.WriteLine(extensionSerialized);

        Console.WriteLine("-----------");

        string allExtensionsSerialized =

                JsonSerializer.Serialize(

                    allExtensions, allExtensions.GetType());

        Console.WriteLine(allExtensionsSerialized);

    }

}

​

public abstract class Extension

{

    public string Name { get; protected internal set; }

}

​

public class DerivedExtensionA : Extension

    {

        public DerivedExtensionA()

        {

            this.Name = "DerivedExtensionA";

            Properties = new Dictionary<string, string>();

        }

​

        public Dictionary<string, string> Properties { get; protected internal set; }

    }

​