incoming_controller.rb

module API
  module Private
    class IncomingController < ApplicationController
      attr_writer :payload

      respond_to :json

      def receive
        key = payload.keys.first
        object = {'charity' => Charity}.fetch(key).new payload[key]
        object.save
      end

      def payload
        @payload ||= ActiveSupport::JSON.decode params[:payload]
      end

      class Charity
        attr_accessor :name, :persistance

        def initialize attributes = {}
          self.persistance = attributes.delete(:persistance) { ::Charity.new }
          attributes.slice(*accepted_attributes).each do |attr, value|
            self.send "#{attr}=", value
          end if attributes
        end

        def accepted_attributes
          [:name]
        end

        def save
          persistance.name = name
          persistance.save
        end
      end
    end
  end
end

This controller is responsible for taking an incoming request from a known source. Instead of using attr_accessible I am thinking of introducing a class that sits between the incoming request and the persistance model.