JsonConverterAttribute on a class

public class UserConverter : JsonConverter
{
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        User user = (User)value;

        writer.WriteValue(user.UserName);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        User user = new User();
        user.UserName = (string)reader.Value;

        return user;
    }

    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(User);
    }
}

[JsonConverter(typeof(UserConverter))]
public class User
{
    public string UserName { get; set; }
}

User user = new User
{
    UserName = @"domain\username"
};

string json = JsonConvert.SerializeObject(user, Formatting.Indented);

Console.WriteLine(json);
// "domain\\username"