The July release of ArcGIS Online included a new security feature which allows you to limit the usage of a service item, you have added or created, to only those applications which you want to have access. This allows you to easily make the service available in specific public applications while preventing access by other applications or users. Information on adding secured services can be found in the ArcGIS Online help.
This has allowed us to simplify our security guidance for the use of the Esri UK Online premium data services (such as OS MasterMap). You no longer need to use long-lived tokens to make the premium data secure when using in public facing applications.