class ActionDispatch::Cookies::SignedCookieJar

def [](name)
  if signed_message = @parent_jar[name]
    verify(signed_message)
  end
end

def []=(name, options)
  if options.is_a?(Hash)
    options.symbolize_keys!
    options[:value] = @verifier.generate(options[:value])
  else
    options = { :value => @verifier.generate(options) }
  end
  raise CookieOverflow if options[:value].size > MAX_COOKIE_SIZE
  @parent_jar[name] = options
end

def initialize(parent_jar, key_generator, options = {})
  @parent_jar = parent_jar
  @options = options
  secret = key_generator.generate_key(@options[:signed_cookie_salt])
  @verifier   = ActiveSupport::MessageVerifier.new(secret)
end

def verify(signed_message)
  @verifier.verify(signed_message)
rescue ActiveSupport::MessageVerifier::InvalidSignature
  nil
end