.Net 4 Web API receiving NULL data in parameters

I am new to the Web API writing the RESTFul Web Api service in .NET 4. I have set up a controller for the class that I am calling Authentication. The problem I am facing is that when I send or put JSON data to the web api service, my handlers in the controller are called, but the parameter objects have NULL values ​​in them. I can successfully get the data, but Post and Put create empty parameter objects.

I tested the client application and Fiddler and get the same result. Here is what I am sending from Fiddler:

Action: PUT
URI: http://127.0.0.1:81/Authentication/xyz/
HTTP Version: HTTP/1.1
Request Headers:
User-Agent: Fiddler
Host: 127.0.0.1:81
Content-Type: application/json; charset=utf-8
Content-Length: 75
Request Body:
{"hashvalue":"kbVFNeBbNHmYQXXlS6d7Ag==","password":"test","username":"dan"}

When I set a breakpoint in the Put handler in the authentication controller:

    public void Put(string IDstring, Authentication value)
    {

    }

In the viewport, I get the following:

IDstring                    null    string
value   {bbsRESTResources.Authentication}   bbsRESTResources.Authentication
    hashvalue   null    string
    password    null    string
    username    null    string

my authentication class is as follows:

namespace bbsRESTResources
{
    public class Authentication
    {
        public string username;
        public string password;
        public string hashvalue;
    }
}

my route is as follows:

        routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );

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