gistfile1.cs

using System;
using System.Collections.Generic;
using Newtonsoft.Json;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var dict = new Dictionary<string, string>();
            dict.Add("username", "test");
            dict.Add("name", "test");

            var serialized = JsonConvert.SerializeObject(dict);
            Console.WriteLine(serialized); //= { "username": "test", "name": "test" }

            var dummy = JsonConvert.DeserializeObject<Dictionary<string, string>>(serialized);
            Console.WriteLine(2 == dummy.Count); //= True

            Console.ReadKey();
        }
    }
}