WCF BodyStyle WrappedRequest doesn't work for incoming JSON param?

I've been working on getting a RESTful WCF service to both accept a JSON as a parameter and return some JSON.

This is my service:

    [OperationContract]
    [WebInvoke(
        Method="POST",
        BodyStyle = WebMessageBodyStyle.WrappedRequest,
        RequestFormat = WebMessageFormat.Json,
        ResponseFormat = WebMessageFormat.Json,
        UriTemplate = "Authenticate")]
    public AuthResponse Authenticate(AuthRequest data)
    {
        AuthResponse res = new AuthResponse();
        if (data != null)
        {
            Debug.WriteLine(data.TokenId);
            res.TokenId = new Guid(data.TokenId);
        }
        return res;
    }

The above will set data to be null when I pass { AuthRequest: { TokenId = "some guid"} }.

If I set the BodyStyle of the method to be Bare then data is set correctly but I must remove { AuthRequest } from the JSON (which I don't really want to do). Is there any way to get WrappedRequests to work with { AuthRequest: { TokenId = "some guid"} as the JSON?

Thanks.