gistfile1.rb

class User < ActiveRecord::Base

  # Include default devise modules. Others available are:
  # :token_authenticatable, :confirmable, :lockable and :timeoutable
  
  devise :database_authenticatable , :registerable, :recoverable, :rememberable, :trackable, :validatable 
  devise :omniauthable#, :omniauth_providers => [:facebook]
  devise :encryptable, :encryptor => :custom_encryptor
  # Devise: Setup accessible (or protected) attributes for your model
  attr_accessible :email, :password, :password_confirmation, :remember_me

  # Called by user/omniauth_devise_controller#facebook to lookup an existing user for facebook.
  #
  # @omniauth [Hash] Omniauth provider hash @see https://github.com/intridea/omniauth/wiki/Auth-Hash-Schema 
  # @user [User] The current logged in user.
  def self.find_for_facebook_oauth(omniauth, user)
    user = User.find_or_initialize_by_fb_uid(omniauth["uid"])
  end

  # Called via devise when new user registration flow begins.
  #
  # @params [Hash] Standard params via rails.
  # @session [Hash] Session containing Oauth hash from devise containing keys for devise.{provider}_data. e.g. "devise.facebook_data". 
  def self.new_with_session(params, session)
    super.tap do |user|
      if data = session["devise.facebook_data"]
        user.email = data["extra"]["user_hash"]["email"]
        user.fb_uid = data["uid"].to_i
        user.name = data["extra"]["user_hash"]["name"]
      end
    end 
  end

  # Overwritten from Devise to turn off password validations for Oauth'd users.
  def password_required?
    return false if oauth?
    # standard validation requirements from Devise
    !persisted? || !password.nil? || !password_confirmation.nil?
  end

  def oauth?
    (!fb_uid.blank?)
  end

end
class UsersDeviseController < Devise::RegistrationsController

  def facebook
    @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"]
      # No existing user create them and redirect to home page.
      data = env["omniauth.auth"]

      user = User.new
      user.email = data["extra"]["user_hash"]["email"]
      user.fb_uid = data["uid"].to_i
      user.name = data["extra"]["user_hash"]["name"]
      user.save!

      set_flash_message :notice, :signed_up
      sign_in_and_redirect user, :event => :signed_up 
      
    end
  end
end