PARC (Principal, Action, Resource, Context) is the shape of an authorization request: who is asking to do what to which resource in what context. Parc models that request and the decision over it, independent of any policy framework.

A pipeline prepares the request, then one decision point judges it, so a policy is declared once and driven from any entry point.

• Parc.Request: the Principal/Action/Resource/Context request.
• Parc.RequestPreparer: a step that enriches the request or aborts with an error, but cannot decide a verdict.
• Parc.PolicyDecider: the decision point that returns an allow, deny, challenge, or error verdict.
• Parc.Pipeline: runs the preparers, then the decider.

Declare a policy pipeline, then run a request through it:

defmodule MyApp.Policy do
  use Parc.Pipeline

  prepare MyApp.Preparers.Clock, key: :now
  decide MyApp.Decider
end

MyApp.Policy.run(request)

Preparers run in declaration order; the first {:error, _} short-circuits and skips the decider. A pipeline has exactly one decider, enforced at compile time.

Add parc to your dependencies in mix.exs:

def deps do
  [
    {:parc, "~> 0.1"}
  ]
end

The API reference is at hexdocs.pm/parc.