01. Gemfile

gem 'pg'
group :development do
	gem 'ruby-debug'
end
gem 'rake', '~> 0.8.7'
gem 'devise'
gem 'oa-oauth', :require => 'omniauth/oauth'
gem 'omniauth'
gem 'haml'
gem 'dynamic_form'
gem 'sass'
gem 'jquery-rails'
gem 'cancan'
gem 'uuidtools'

02. Generate migration and add authorization model

rails generate devise:install
rails generate devise user
rails g migration add_name_to_users name:string
rails g model authorization provider:string uid:string user_id:integer token:string secret:string name:string link:string

_devise_create_users.rb

# /db/migrate/<timestamp>_devise_create_users.rb

class DeviseCreateUsers < ActiveRecord::Migration
  def self.up
    create_table(:users) do |t|
      t.database_authenticatable :null => false
      t.recoverable
      t.rememberable
      t.trackable
      t.encryptable
      t.confirmable
      t.lockable :lock_strategy => :failed_attempts, :unlock_strategy => :both
      t.token_authenticatable
      t.timestamps
    end
    add_index :users, :email,                :unique => true
    add_index :users, :reset_password_token, :unique => true
    add_index :users, :confirmation_token,   :unique => true
    add_index :users, :unlock_token,         :unique => true
    add_index :users, :authentication_token, :unique => true
  end

  def self.down
    drop_table :users
  end
end

authorization.rb

# app/models/authorization.rb

class Authorization < ActiveRecord::Base
  
  belongs_to :user
  
end

development.rb

# config/environments

config.action_mailer.perform_deliveries    = true
config.action_mailer.raise_delivery_errors = true
config.action_mailer.default_url_options = { :host => 'localhost:3000' }
HOST = 'localhost:3000'
ADMIN_EMAIL_FROM = ""
PONY_VIA_OPTIONS = {
  :address => 'smtp.gmail.com', 
  :port => '587',
  :enable_starttls_auto => true,
  :user_name => '',
  :password => '',
  :authentication => :plain,
  :domain => "localhost.localdomain" }

devise.rb

# app/config/initializers/devise.rb

Devise.setup do |config|
...
  config.sign_out_via = :get
...
  config.omniauth :facebook, "KEY", "SECRET"
  config.omniauth :twitter, "KEY", "SECRET"
  config.omniauth :linked_in, "KEY", "SECRET"
...
end

omniauth_callbacks_controller.rb

class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
  
  require 'uuidtools'
  
  def facebook
    oauthorize "Facebook"
  end
  
  def twitter
    oauthorize "Twitter"
  end
  
  def linked_in
    oauthorize "LinkedIn"
  end
  
  def passthru
    render :file => "#{Rails.root}/public/404.html", :status => 404, :layout => false
  end
  
private

  def oauthorize(kind)
    @user = find_for_ouath(kind, env["omniauth.auth"], current_user)
    if @user
      flash[:notice] = I18n.t "devise.omniauth_callbacks.success", :kind => kind
      session["devise.#{kind.downcase}_data"] = env["omniauth.auth"]
      sign_in_and_redirect @user, :event => :authentication
    end    
  end

  def find_for_ouath(provider, access_token, resource=nil)
    user, email, name, uid, auth_attr = nil, nil, nil, {}
    case provider
    when "Facebook"
      uid = access_token['uid']
      email = access_token['extra']['user_hash']['email']
      auth_attr = { :uid => uid, :token => access_token['credentials']['token'], :secret => nil, :name => access_token['extra']['user_hash']['name'], :link => access_token['extra']['user_hash']['link'] }
    when "Twitter"
      uid = access_token['extra']['user_hash']['id']
      name = access_token['user_info']['name']
      auth_attr = { :uid => uid, :token => access_token['credentials']['token'], :secret => access_token['credentials']['secret'], :name => name, :link => "http://twitter.com/#{name}" }
    when 'LinkedIn'
      uid = access_token['uid']
      name = access_token['user_info']['name']
      auth_attr = { :uid => uid, :token => access_token['credentials']['token'], :secret => access_token['credentials']['secret'], :name => name, :link => access_token['user_info']['public_profile_url'] }
    else
      raise 'Provider #{provider} not handled'
    end
    if resource.nil?
      if email
        user = find_for_oauth_by_email(email, resource)
      elsif uid && name
        user = find_for_oauth_by_uid(uid, resource)
        if user.nil?
          user = find_for_oauth_by_name(name, resource)
        end
      end
    else
      user = resource
    end
    
    auth = user.authorizations.find_by_provider(provider)
    if auth.nil?
      auth = user.authorizations.build(:provider => provider)
      user.authorizations << auth
    end
    auth.update_attributes auth_attr
    
    return user
  end

  def find_for_oauth_by_uid(uid, resource=nil)
    user = nil
    if auth = Authorization.find_by_uid(uid.to_s)
      user = auth.user
    end
    return user
  end

  def find_for_oauth_by_email(email, resource=nil)
    if user = User.find_by_email(email)
      user
    else
      user = User.new(:email => email, :password => Devise.friendly_token[0,20]) 
      user.save
    end
    return user
  end
  
  def find_for_oauth_by_name(name, resource=nil)
    if user = User.find_by_name(name)
      user
    else
      user = User.new(:name => name, :password => Devise.friendly_token[0,20], :email => "#{UUIDTools::UUID.random_create}@host")
      user.save false
    end
    return user
  end

end

registrations_controller.rb

class RegistrationsController < Devise::RegistrationsController

  def update
    if params[resource_name][:password].blank?
      params[resource_name].delete(:password)
      params[resource_name].delete(:password_confirmation) if params[resource_name][:password_confirmation].blank?
    end
    # Override Devise to use update_attributes instead of update_with_password.
    # This is the only change we make.
    if resource.update_attributes(params[resource_name])
      set_flash_message :notice, :updated
      # Line below required if using Devise >= 1.2.0
      sign_in resource_name, resource, :bypass => true
      redirect_to after_update_path_for(resource)
    else
      clean_up_passwords(resource)
      render_with_scope :edit
    end
  end
  
end

routes.rb

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

user.rb

# app/models/user.rb

class User < ActiveRecord::Base

  devise :database_authenticatable, :registerable, :recoverable, :rememberable, :trackable, :validatable, :confirmable, :omniauthable
  attr_accessible :email, :name, :password, :password_confirmation, :remember_me
  has_many :authorizations, :dependent => :destroy

end