setting up ssl on devise

I'd like to require ssl authentication for the user resource on devise. I was expecting that to be as simple as it is in rails, like:

  devise_for :users, :constraints => { :protocol => "https" }

Also, I couldn't find any documentation on devise's github, though I've found some dead links pointing to it at the google groups.

Does anybody has a hint on how to get it working easily? I thought I'd be simple, given the popularity of the plugin