Simple authorization module with Rails

I created a simple Authorization module with Rails. I found that there are other authorization systems, such as CanCanCan, but they grant permissions at Model level and, for this particular website I am developing, it is more convenient to authorize at Controller level.

The idea is simple: the permissions are stored in a YAML file in the config directory and a function checks if the combination of admin_role, controller and action exist in the config file. There is also a wildcard :all.

# app/controllers/admins/base_controller.rb
class Admins::BaseController < ApplicationController

  include Admins::AuthorizationHelper

  before_action :authorize_admin

  ...

end

# app/helpers/admin/authorization_helper.rb
module Admins::AuthorizationHelper

  private

  def authorize_admin
    unless is_authorized? params[:controller], params[:action]
      refuse_access_to_admin_site
    end
  end

  def is_authorized?(controller, action)
    permissions = Rails.application.config_for :admin_auth
    authority = current_admin.authority

    if permissions[authority].nil?
      false
    elsif permissions[authority] == ['all']
      true
    elsif permissions[authority][controller].nil?
      false
    elsif permissions[authority][controller] == ['all']
      true
    elsif permissions[authority][controller].include? action
      true
    else
      false
    end
  end

  def refuse_access_to_admin_site
    flash[:error] = 'Permission denied'

    if request.referer.present?
      redirect_to :back
    else
      redirect_to admins_products_path
    end
  end

end

# config/admin_auth.yml   
defaults: &defaults
    super_admins:
        - all
    admins:
        admins/shops:
            - index
            - show_used_history
        admins/products:
            - index
        admins/prescriptions:
            - all
        admins/products:
            - index
    operators:
        admins/products:
            - index
        admins/prescriptions:
            - all
        admins/shipments:
            - index
            - show
test:
    <<: *defaults
development:
    <<: *defaults
staging:
    <<: *defaults
production:
    <<: *defaults

There’s a lot of repeated code in that long if..else. Here’s an idea (code not tested) for shortening it up:

def is_authorized?(controller, action)
  permissions = Rails.application.config_for :admin_auth
  authority = current_admin.authority

  global_auth = permissions.fetch(authority, [])
  return true if global_auth.include? 'all'

  # Note the implicit assumption in this code, and the original code,
  # that global_auth is a Hash if we have not already returned

  ctrl_auth = global_auth.fetch(controller, [])
  ctrl_auth.include? 'all' || ctrl_auth.include? action
end

Please see the inline comment for an assumption your making about the config data.

At a higher level, the deeper reason this code has to be overly complicated and do nil checks and checks for different kinds of data (array or hash) is because the config data structure has no regularity.

The real fix here is probably to wrap that returned data structure in an object that regularizes it, essentially using something similar to the NullObject pattern. So that your code could then read like this:

permissions = Rails.application.config_for :admin_auth
permissions = ConfiguredPermissions.new permissions

permissions.global_access? || permissions.for?(controller, action)

You can also avoid the if..else in your redirect method:

  def refuse_access_to_admin_site
    flash[:error] = 'Permission denied'

    location = request.referer.present? ? :back : admins_products_path
    redirect_to location
  end