static void TrySetCanceled(RequestResponseStateLookup.State state)
 {
     if (state.CancellationToken.IsCancellationRequested)
     {
         state.TaskCompletionSource.TrySetCanceled();
     }
 }
 public static void RegisterCancellationToken(this ExtendableOptions options, CancellationToken cancellationToken)
 {
     var extensions = options.GetExtensions();
     RequestResponseStateLookup.State state;
     if (extensions.TryGet(out state))
     {
         state.CancellationToken = cancellationToken;
     }
     else
     {
         state = new RequestResponseStateLookup.State
         {
             CancellationToken = cancellationToken
         };
     }
     extensions.Set(state);
 }