[InheritedExport]
    public interface IOperationBehaviorExtender
    {
        string Action { get; }
        bool BeforeInvoke(string action, object[] inputs, out string faultMessage);
        void AfterInvoke(string action, object[] inputs, ref object[] outputs, ref object returnValue);
        bool ValidateBeforeCall(string action, object[] inputs, out string message);
        void AfterCall(string action, object[] outputs, object returnValue, object correlationState);
    }

Web Extensibility Download Part 2 -  Making the Part discoverable

C#