using System;

using System.Text.Json;

using System.Text.Json.Nodes;

using System.Text.Json.Serialization;

​

var json = @"

{""a"":2,

""b"":true,

""c"":""something""

}";

​

var value = JsonSerializer.Deserialize<MyClass>(json);

Console.WriteLine(JsonSerializer.Serialize(value));

​

public class MyClass

{

    public int a {get;set;}

    [JsonExtensionData]

    public JsonObject? Extensions { get; set; }

}