Defining a custom JsonConverter and using it with the built-in JsonConverterAttribute

Message.cs

public class Message
{
  [JsonConverter(typeof(SHA256StringJsonConverter))]
  public string Password { get; set; }
}
  

SHA256StringJsonConverter.cs

public class SHA256StringJsonConverter : JsonConverter
{
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var hashedPassword = value.ToString().ToSHA256Hash();
        writer.WriteValue(hashedPassword);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        // The value should be hashed already. Nothing to do here.
        return reader.Value;
    }

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