ソースコード抜粋
# Rack::Session::Cookie provides simple cookie based session management.
# By default, the session is a Ruby Hash stored as base64 encoded marshalled
# data set to :key (default: rack.session). The object that encodes the
# session data is configurable and must respond to +encode+ and +decode+.
# Both methods must take a string and return a string.
#
# When the secret key is set, cookie data is checked for data integrity.
# The old secret key is also accepted and allows graceful secret rotation.
#
# Example:
#
# use Rack::Session::Cookie, :key => 'rack.session',
# :domain => 'foo.com',
# :path => '/',
# :expire_after => 2592000,
# :secret => 'change_me',
# :old_secret => 'also_change_me'
#
# All parameters are optional.
#
# Example of a cookie with no encoding:
#
# Rack::Session::Cookie.new(application, {
# :coder => Rack::Session::Cookie::Identity.new
# })
#
# Example of a cookie with custom encoding:
#
# Rack::Session::Cookie.new(application, {
# :coder => Class.new {
# def encode(str); str.reverse; end
# def decode(str); str.reverse; end
# }.new
# })
#
