gistfile1.rb

# user.rb

class User < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :token_authenticatable, :encryptable, :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable, :omniauthable

  # Setup accessible (or protected) attributes for your model
  attr_accessible :email, :password, :password_confirmation, :remember_me

  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

    def self.new_with_session(params, session)
    super.tap do |user|
      if data = session["devise.facebook_data"] && session["devise.facebook_data"]["extra"]["user_hash"]
        user.email = data["email"]
      end
    end
  end

end


# routes.rb

  devise_for :users, :controllers => { :omniauth_callbacks => "users/omniauth_callbacks" }


# users/omniauth_callbacks_controller.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

# config/initializers/devise.rb

  config.omniauth :facebook, 'appid', 'token', :scope => %w(email), :client_options => {:ssl => {:ca_file => '/home/solars/projects/test/rails3-blog/certs/cacert.pem'}}