public TActivity AuthorizedBy <T>(Action <T> postBuildExpression) where T : IActivityAuthorizer
        {
            AuthorizerTypes.Add(new KeyValuePair <Type, Action <IActivityAuthorizer> >(typeof(T), (a) => postBuildExpression.Invoke((T)a)));

            return((TActivity)this);
        }
 public TActivity AuthorizedBy <T>() where T : IActivityAuthorizer
 {
     AuthorizerTypes.Add(new KeyValuePair <Type, Action <IActivityAuthorizer> >(typeof(T), null));
     return((TActivity)this);
 }