Calling a WCF service with HttpWebRequest having custom authentication

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C#

WCF

There is an answered question here but my case is a little different.

1) it's not a REST service
2) it has custom username-password validation

what I need is to call the service using HttpWebRequest "POST" method with JSON request and response format; this is what I have so far...

public class Service : IService
{
    public string SayHello(string name)
    {
        return String.Format("Hello {0}!", name);
    }
}

and

public interface IService
{
    [OperationContract]
    string SayHello(string name);
}

What I need to have is something like this...

HttpWebRequest request = WebRequest.Create("http://localhost:56779/BeSTService.svc/SayHello") as HttpWebRequest;
            string parameters = "{\"name\":\"Umais\"}"; // or any other way to send parameters
            request.Method = "POST";
            request.ContentLength = 0;
            request.ContentType = "application/json";
            if (!string.IsNullOrEmpty(parameters))
            {
                byte[] byteArray = Encoding.UTF8.GetBytes(parameters);
                request.ContentLength = byteArray.Length;
                Stream dataStream = request.GetRequestStream();
                dataStream.Write(byteArray, 0, byteArray.Length);
                dataStream.Close();
            }
            HttpWebResponse response = (HttpWebResponse)request.GetResponse();

I need to use wsHttpBinding as I'm unable to implement the same authentication in webHttpBinding. The wsHttpBinding is working (with authentication) in windows application; however, I need to call this service as HttpWebResponse,HttpWebRequest as well. Please help me out here! I get "Bad Request" error.