title: No secret option provided to Rack::Session::Cookie warning?
body: <p>I am running Rails 3.2.3, Ruby 1.9 under Fedora 17.  I get this warning, when I run <code>rails s</code>, and how do I fix?</p>
  
  <blockquote>
    <p>SECURITY WARNING: No secret option provided to Rack::Session::Cookie.
       This poses a security threat. It is strongly recommended that you
       provide a secret to prevent exploits that may be possible from crafted
       cookies. This will not be supported in future versions of Rack, and
       future versions will even invalidate your existing user cookies.</p>
  </blockquote>