How I integrated cancan into a widget

form_widget.rb

class MenuEditor::Page::FormWidget < Apotomo::Widget
  # Step 1: make sure the current_user variable (or something like it) is available for use
  include Devise::Controllers::Helpers
  helper_method :current_user
  responds_to_event :submit

  def display
    ...
  end

  def submit(event)
    # Step 3: call `current_ability.authorize!` like you would `authorize!` in a controller
    current_ability.authorize! :manage, @current_site
    @nav_item = @current_site.nav_items.new params[:nav_item]
    ...
  end

  private

  def setup!(*)
    @current_site ||= options[:current_site]
  end

  # Step 2: instantiate Ability with passing the current_user
  def current_ability
    ::Ability.new current_user
  end
end

You can also add:

def can?(action, object)
  current_ability.can? action, object
end

Then make that method a helper:

helper_method :can?

So that you can do this in your views:

- if can? :purchase, @product