Ruby module for convenient authenticity token generation and usage for any class

authenticity_token.rb

module AuthenticityToken

  def authenticity_token(&block)
    class_inheritable_accessor :authenticity_token_generator
    self.authenticity_token_generator = block
    include InstanceMethods
  end

  module InstanceMethods

    def authenticity_token
      block = self.class.authenticity_token_generator
      instance_eval(&block)
    end

    def authenticity_token=(token)
      # Does nothing, but avoids errors when used with
      # a web framework like Rails which provides a
      # mass-attribute-update-functionality.
    end

    def authentic?(token)
      authenticity_token == token
    end

  end

end

# Usage example:
#
# class MyClass
#   extend AuthenticityToken
#
#   authenticity_token do
#     Digest::MD5.hexdigest("bacon")
#   end
# end
#
# my = MyClass.new
# my.authenticity_token # => "7813258ef8c6b632dde8cc80f6bda62f"
# my.authentic?("7813258ef8c6b632dde8cc80f6bda62f") # => true
# my.authentic?("wurst") # => false