application_controller.rb

class ApplicationController < ActionController::Base

  # Includes Authorization mechanism
  include Pundit

  # Prevent CSRF attacks by raising an exception.
  # For APIs, you may want to use :null_session instead.
  protect_from_forgery with: :exception

  # Globally rescue Authorization Errors in controller.
  # Returning 403 Forbidden if permission is denied
  rescue_from Pundit::NotAuthorizedError, with: :permission_denied

  # Enforces access right checks for individuals resources
  after_filter :verify_authorized, :except => :index

  # Enforces access right checks for collections
  after_filter :verify_policy_scoped, :only => :index


  private

  def permission_denied
    head 403
  end

end

person_policy.rb

class PersonPolicy < ApplicationPolicy

  class Scope < Struct.new(:user, :scope)
    def resolve
      scope
    end
  end
end

pundit_metaprograming_acces_rights.rb

class ApplicationPolicy
  attr_reader :user, :record

  def initialize(user, record)
    @user = user
    @record = record
  end

  def user_activities
    @user.roles.select(:activities).distinct.map(&:activities).flatten
  end

  def inferred_activity(method)
    "#{@record.class.name.downcase}:#{method.to_s}"
  end

  def method_missing(name,*args)
    if name.to_s.last == '?'
      user_activities.include?(inferred_activity(name.to_s.gsub('?','')))
    else
      super
    end
  end


  def scope
    Pundit.policy_scope!(user, record.class)
  end
end