How to add a UsernameToken to the RequestSoapContext property of web service proxy class

Question

I have a service that I have referenced which creates a proxy class "MyWebService". However when I use that class its object doesnt seem to have the RequestSoapContext property. Here below is how I was expecting to consume the service:

            MyWebService objWS = new MyWebService();
            UsernameToken token = new UsernameToken("User","Password", PasswordOption.SendPlainText);
            objWS.RequestSoapContext.Security.Timestamp.TtlInSeconds = 60;
            objWS.RequestSoapContext.Security.Tokens.Add(token);
            objWS.RequestSoapContext.Security.MustUnderstand = false;

Is there some configuration/modification that I need to make to the generated proxy class so that I can get the RequestSoapContext in there proxy class or do I need to do something on service side?

Thanks for your time...