How to use arguments in policies

  policies do
    bypass action_type(:create) do
      authorize_if always()
    end

    bypass action(:join) do
      authorize_if expr(invite_code == ^arg(:invite_code))
    end

    policy always() do
      authorize_if expr(exists(members, id == ^actor(:id)))
    end
  end
...
  actions do
    defaults [:update, :destroy]

    read :read do
      primary? true
    end

    create :create do
      accept [:name]
    end

    update :join do
      argument :name, :string do
        allow_nil? false
      end

      argument :invite_code, :uuid do
        allow_nil? false
      end

      change manage_relationship :name, :members,
        value_is_key: :name,
        type: :create
    end
  end

  policies do
    policy always() do
      authorize_if always()
    end
  end

  actions do
    defaults [:read, :create, :update, :destroy]
  end

  attributes do
    uuid_primary_key :id

    attribute :room_id, :uuid do
      allow_nil? false
    end

    attribute :name, :string do
      allow_nil? false
    end

    timestamps()
  end