The PARC (Principal, Action, Resource, Context) authorization request: the data a
Parc.PolicyDecider decides on. An adapter builds it, the declared preparers
transform it, and the decider evaluates it.
Fields:
:principal: who is asking;nilwhen anonymous.:action: what is being attempted (action/0); required.:resource: what it acts on (resource/0); required.:context: facts a preparer adds for the decider;%{}by default.