actionview/lib/action_view/helpers/csrf_helper.rb

module ActionView
  # = Action View CSRF Helper
  module Helpers
    module CsrfHelper
      # Returns meta tags "csrf-param" and "csrf-token" with the name of the cross-site
      # request forgery protection parameter and token, respectively.
      #
      #   <head>
      #     <%= csrf_meta_tags %>
      #   </head>
      #
      # These are used to generate the dynamic forms that implement non-remote links with
      # <tt>:method</tt>.
      #
      # Note that regular forms generate hidden fields, and that Ajax calls are whitelisted,
      # so they do not use these tags.
      def csrf_meta_tags
        if protect_against_forgery?
          [
            tag('meta', :name => 'csrf-param', :content => request_forgery_protection_token),
            tag('meta', :name => 'csrf-token', :content => form_authenticity_token)
          ].join("\n").html_safe
        end
      end

      # For backwards compatibility.
      alias csrf_meta_tag csrf_meta_tags
    end
  end
end