Question

I am using Railscast Episode # 250 to implement authentication from scratch. However, now I want to implement Facebook login. From googling I’ve found that OmniAuth and Devise are the prime contenders to do this in Rails

However, this example page is confusing me: https://github.com/plataformatec/devise/wiki/OmniAuth:-Overview

It states:

With Rails 3.0.3, use this in your Gemfile instead if rails is having
trouble loading oauth core:

gem “omniauth”

Next, you need to declare the provider in your
config/initializers/devise.rb:

config.omniauth :facebook, “APP_ID”, “APP_SECRET”

Question

Are omniauth and devise interelated?

What should I do to implement Facebook login in my authentication based on Railscast 250

Answer 1

In your specific case you can think that Devise allows your application to authenticate users using a form (ex: by using an email and password) or an authentication token, Omniauth allows your application to “speak” to the Facebook servers to authenticate a user. In other words Omniauth sits on top of Devise and extends the number of ways your user can authenticate.

To implement Facebook login you need to:

0) configure devise: just follow this: https://github.com/plataformatec/devise/wiki/OmniAuth:-Overview

1) expose a link in your view that when clicked by the user will tell Omniauth to start “speaking” to the Facebook server.

=link_to image_tag("facebook_64.png", :size => "64x64", :alt => "Facebook"), user_omniauth_authorize_path(:facebook, :display=>"dialog"),  :title=>"Facebook"

2) At one point the Facebook server will call you app so you have to implement a controller to respond to Facebook

class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
  before_filter { @omniauth_hash = env["omniauth.auth"] }

      # This method is responsible to create a registration_hash given an
      # omniaauth_hash
      # schama: https://github.com/intridea/omniauth/wiki/Auth-Hash-Schema
      def self.build_registration_hash(omniauth_hash={})
        if (omniauth_hash["provider"].downcase.eql?("facebook"))
          provider  = "facebook"
          # catch any excpetions thrown by code just to make sure we can continue even if parts of the omnia_has are missing
          begin
            first_name = omniauth_hash['user_info']['first_name']
            last_name  = omniauth_hash['user_info']['last_name']
            sex        = omniauth_hash.fetch('extra', {}).fetch('user_hash',{})['gender']
            birthday   = Date.strptime(omniauth_hash.fetch('extra', {}).fetch('user_hash', {})['birthday'],'%m/%d/%Y') if omniauth_hash.fetch('extra', {}).fetch('user_hash', {})['birthday']
            if omniauth_hash.fetch('extra', {}).fetch('user_hash', {})['timezone']
              utc_offset_in_hours = (omniauth_hash.fetch('extra', {}).fetch('user_hash', {})['timezone']).to_i 
              time_zone = (ActiveSupport::TimeZone[utc_offset_in_hours]).name
            else
              time_zone = nil
            end
            locale    = omniauth_hash.fetch('extra', {}).fetch('user_hash', {})['locale'] 
            home_town = omniauth_hash.fetch('extra', {}).fetch('user_hash', {}).fetch('location', {})['name']
            if omniauth_hash.fetch('user_info', {})['image']
              photo_url = (omniauth_hash.fetch('user_info', {})['image']).gsub("=square","=large")   #http://graph.facebook.com/531564247/picture?type=square
            else
              photo_url = nil
            end
          rescue => ex
            logger.error("Error while parsing facebook auth hash: #{ex.class}: #{ex.message}")
            sex       = nil
            birthday  = nil
            time_zone = nil
            locale    = nil
            home_town = nil
            photo_url = nil  
          end
        elsif omniauth_hash['uid'].downcase.include?("google.com")
          provider  = "google"
          if omniauth_hash['user_info']['first_name'] and omniauth_hash['user_info']['last_name']
            first_name = omniauth_hash['user_info']['first_name'] 
            last_name  = omniauth_hash['user_info']['last_name']
          elsif omniauth_hash['user_info']['name'] 
            first_name  = omniauth_hash['user_info']['name'].split(' ')[0]
            last_name  = omniauth_hash['user_info']['name'].split(' ')[1]
          else
            first_name = nil
            last_name  = nil
          end
          sex       = nil
          birthday  = nil
          time_zone = nil
          locale    = nil
          home_town = nil
          photo_url = nil
        elsif omniauth_hash['uid'].downcase.include?("yahoo.com")
          provider = "yahoo"
          if omniauth_hash['user_info']['first_name'] and omniauth_hash['user_info']['last_name']
            first_name = omniauth_hash['user_info']['first_name'] 
            last_name  = omniauth_hash['user_info']['last_name']
          elsif omniauth_hash['user_info']['name'] 
            first_name  = omniauth_hash['user_info']['name'].split(' ')[0]
            last_name  = omniauth_hash['user_info']['name'].split(' ')[1]
          else
            first_name = nil
            last_name  = nil
          end
          sex       = nil
          birthday  = nil
          time_zone = nil
          locale    = nil
          home_town = nil
          photo_url = nil
        elsif omniauth_hash['uid'].downcase.include?("aol.com")
          if omniauth_hash['user_info']['first_name'] and omniauth_hash['user_info']['last_name']
            first_name = omniauth_hash['user_info']['first_name'] 
            last_name  = omniauth_hash['user_info']['last_name']
          elsif omniauth_hash['user_info']['name'] 
            first_name  = omniauth_hash['user_info']['name'].split(' ')[0]
            last_name  = omniauth_hash['user_info']['name'].split(' ')[1]
          else
            first_name = nil
            last_name  = nil
          end
          provider = "aol"
          sex       = nil
          birthday  = nil
          time_zone = nil
          locale    = nil
          home_town = nil
          photo_url = nil     
        else
          provider = "open_id"
          if omniauth_hash['user_info']['first_name'] and omniauth_hash['user_info']['last_name']
            first_name = omniauth_hash['user_info']['first_name'] 
            last_name  = omniauth_hash['user_info']['last_name']
          elsif omniauth_hash['user_info']['name'] 
            first_name  = omniauth_hash['user_info']['name'].split(' ')[0]
            last_name  = omniauth_hash['user_info']['name'].split(' ')[1]
          else
            first_name = nil
            last_name  = nil
          end
          sex       = nil
          birthday  = nil
          time_zone = nil
          locale    = nil
          home_town = nil
          photo_url = nil
        end

       h = {
          :provider   => provider,
          :email      => omniauth_hash['user_info']['email'],
          :profile_attributes => {
             :first_name => first_name ,
             :last_name  => last_name,
             :avatar_url  => photo_url,
             :sex        => sex,
             :birthday   => birthday,
             :time_zone  => time_zone,
             :locale     => locale,
             :location  => home_town
          }
        }
      end

      def process_callback

        # The registration hash isolates the rest of the code from learning all the different structures 
        # of the omnia_hash
        registration_hash = Users::OmniauthCallbacksController.build_registration_hash(@omniauth_hash)
        logger.debug(registration_hash.to_yaml)

        # Set the @user to nil 
        @user = nil 

        # Find if an authentication token for this provider and user id already exists
        authentication = Authentication.find_by_provider_and_uid(@omniauth_hash['provider'], @omniauth_hash['uid'])
        if authentication     # We found an authentication
          if user_signed_in? && (authentication.user.id != current_user.id)
            flash[:error] = I18n.t "controllers.omniauth_callbacks.process_callback.error.account_already_taken", 
            :provider => registration_hash[:provider].capitalize, 
            :account => registration_hash[:email]
            redirect_to edit_user_account_path(current_user)
            return
          end
        else
          # We could not find the authentication than create one
          authentication = Authentication.new(:provider => @omniauth_hash['provider'], :uid => @omniauth_hash['uid'])
          if user_signed_in?   
            authentication.user = current_user
          else
            registration_hash[:skip_confirmation] = true
            authentication.user = User.find_by_email(registration_hash[:email]) || User.create_user(registration_hash)
          end
        end

        @user = authentication.user
        # save the authentication 
        authentication.token = @omniauth_hash
        authentication.provider_name = registration_hash[:provider]
        authentication.provider_username = registration_hash[:email]

        if !authentication.save
          logger.error(authentication.errors)
        end

        # If a user is signed in then he is trying to link a new account
        if user_signed_in?
          if authentication.persisted? # This was a linking operation so send back the user to the account edit page  
            flash[:success] = I18n.t "controllers.omniauth_callbacks.process_callback.success.link_account", 
                                    :provider => registration_hash[:provider].capitalize, 
                                    :account => registration_hash[:email]
          else
            flash[:error] = I18n.t "controllers.omniauth_callbacks.process_callback.error.link_account", 
                                   :provider => registration_hash[:provider].capitalize, 
                                   :account => registration_hash[:email],
                                   :errors =>authentication.errors
          end  
          redirect_to edit_user_account_path(current_user)
        else
          # This was a sign in operation so sign in the user and redirect it to his home page
          if @user.persisted? && authentication.persisted?
            flash[:success] = I18n.t "controllers.omniauth_callbacks.process_callback.success.sign_in", 
            :provider => registration_hash[:provider].capitalize, 
            :account => registration_hash[:email]
            sign_in_and_redirect(:user,@user)
          else
            session['registration_hash'] = registration_hash
            flash[:error] = I18n.t "controllers.omniauth_callbacks.process_callback.error.sign_in", 
            :provider => registration_hash[:provider].capitalize, 
            :account => registration_hash[:email]

            redirect_to new_registration_users_url

          end
        end
      end

      def facebook
        process_callback  
      end

      def gmail
        process_callback  
      end

Now you will notice that I call a User.create_user(registration_hash). This method implementation will depend on how your app create a user but at the minimum the method has to create a user and assign to it a random password:

def self.create_user(registration_hash)
    logger.info "Creating new user with registration hash: #{registration_hash.to_yaml}"
    unless registration_hash or resigration_hash.empty?
      return nil
    end
    user = User.new
    user.email = registration_hash[:email]
    if registration_hash[:password]
      user.password = registration_hash[:password]
    else
      user.password = Devise.friendly_token[0,20]
    end
    user.password_confirmation = user.password

    # custom app code here...


    if registration_hash[:skip_confirmation] == true
      user.confirm!
    end

    user    
  end

Note: My app support login with other service so I have implemented a table that contain authentication tokens.

Hope this can get you started.