Controller plug to authorize actions based on permissions.

Usage in a controller:

plug VoileWeb.Plugs.Authorize, permissions: %{
  new: ["metadata.manage"],
  create: ["metadata.manage"],
  edit: ["metadata.manage", "metadata.edit"],
  update: ["metadata.manage", "metadata.edit"],
  delete: ["metadata.manage"]
}

If an action is not present in the permissions map, the plug is a no-op. The plug logs authorization attempts (user id, action, required permissions, and whether the attempt was allowed).