How to call devise sign_in and sign_out methods of devise from another controller different from devise?

I have a Ruby on Rails 3.0.7 application and my user authentication with devisebut and I have an alternative sign up and sign in methods, I allow my users to sign up using their Facebook account then I save that login info in my users table the same one that devise uses to register and login users.

Steps

1. ✔ User click on the Facebook button.
2. ✔ I save his info (name and email extracted from Koala) I give the user a generic password.
3. ☐ Login this new user with devise.
4. ✔ Redirect to my main controller.

I'm just missing the 3rd step because I want to keep using the current_user helper and the user_signed_in? helper too.

So how do I tell devise to sign in this user automatically from my other controller?

I saw something like that on this question Devise: Have multiple controllers handle user sessions and it logs my user in but leads me to an blank page...