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The OrderItem directly references the Resource (the Resource Id is part of the OrderItem). However, the Resource does not directly reference Muffins. In fact, the order entry system doesn't care about distinguishing among these items at an entity level. It would be happy knowing the Id, name, and price of the Resource. Only the application that manages coffee beans cares about operating on Coffee entities.
Different applications care about different things. Tightly wiring a model together gets unwieldy and one of the symptoms is the endless stream of ORs in the entity (it could be this OR it could be that OR it could be something else).
The relation between Resource and the items is not explicit, it is assumed. In the case a Mug is purchased, it appears in the service environment as both a Mug and a Resource. This implicit assumption is part of the orchestration agreement between the Starbucks Inventory OSID and the Resource OSID.
Perhaps this can be applied to the authorization dilemma.