class ActionDispatch::Cookies::UpgradeLegacySignedCookieJar

:nodoc:
them using the new key generator to provide a smooth upgrade path.
legacy cookies signed with the old dummy key generator and re-saves
secrets.secret_token and secrets.secret_key_base are both set. It reads
UpgradeLegacySignedCookieJar is used instead of SignedCookieJar if

def [](name) 

def [](name)
  if signed_message = @parent_jar[name]
    deserialize(name, verify(signed_message)) || verify_and_upgrade_legacy_signed_message(name, signed_message)
  end
end