facebook + devise

callback.rb

class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
  def facebook
    # You need to implement the method below in your model
    @user = User.find_for_facebook_oauth(env["omniauth.auth"], current_user)

    if @user.persisted?
      flash[:notice] = I18n.t "devise.omniauth_callbacks.success", :kind => "Facebook"
      sign_in_and_redirect @user, :event => :authentication
    else
      session["devise.facebook_data"] = env["omniauth.auth"]
      redirect_to new_user_registration_url
    end
  end
end

user.rb

def self.find_for_facebook_oauth(access_token, signed_in_resource=nil)
  data = access_token['extra']['user_hash']
  if user = User.find_by_email(data["email"])
    user
  else # Create a user with a stub password. 
    User.create(:email => data["email"], :password => Devise.friendly_token[0,20]) 
  end
end