Custom Invoker to Invoke the operation only if the Token is valid

CustomInvoker.cs

using System;
using System.ServiceModel;
using System.ServiceModel.Dispatcher;

namespace TokenValidator
{
    class CustomInvoker : IOperationInvoker
    {
        private readonly IOperationInvoker defaultInvoker;

        public CustomInvoker(IOperationInvoker defaultInvoker)
        {
            this.defaultInvoker = defaultInvoker;
        }
        public bool IsSynchronous
        {
            get { return defaultInvoker.IsSynchronous; }
        }

        public object[] AllocateInputs()
        {
            return defaultInvoker.AllocateInputs();
        }

        public object Invoke(object instance, object[] inputs, out object[] outputs)
        {
            // Check the value of the Authorized header added by Message Inspector
            if (OperationContext.Current.IncomingMessageProperties.ContainsKey("Authorized"))
            {
                bool allow = (bool)OperationContext.Current.IncomingMessageProperties["Authorized"];
                if (!allow)
                {
                    outputs = null;
                    return null;
                }
            }
            // Otherwise, go ahead and invoke the operation
            return defaultInvoker.Invoke(instance, inputs, out outputs);
        }

        public IAsyncResult InvokeBegin(object instance, object[] inputs, AsyncCallback callback, object state)
        {
            return defaultInvoker.InvokeBegin(instance, inputs, callback, state);
        }

        public object InvokeEnd(object instance, out object[] outputs, IAsyncResult result)
        {
            return defaultInvoker.InvokeEnd(instance, out outputs, result);
        }
    }
}