Rails requires an authenticity token to do form posts back to the server. This helps protect your site against CSRF attacks. In order to handle this requirement the driver looks for two meta tags that must be defined in your page's head.
link_to :controller => 'user_sessions', :action => 'destroy'
# Route match '/log' => "user_sessions#destroy", :as => :logout # View link_to 'Logout', '/logout'