In a rails controller or a helper you can easily read a signed cookie via
Outside that, if you have access to your rails server (which has the secret key), you can use Rack to read the secure cookie string. The default Rails 3/4 session store (cookie store) allows users to read the contents of the session. They may not, however, change or tamper with the session data.
Follow this gist to read a signed cookie/session string.