http://blog.guiltry.com/devise-multiple-provider-with-factory-method-pattern

concrete_product.rb

module FactoryMethod
  # [Role] Product
  class FacebookUser
    def initialize(identity, data)
      @identity = identity
      @data = data
    end

    def create
      @user = User.where(email: @data.info.email)

      # Create the user if it's a new registration
      if @user.blank?
        @user = User.new(
          first_name: @data.info.first_name,
          last_name: @data.info.last_name,
          email: @data.info.email,
          image: @data.info.image,
          gender: @data.extra.raw_info.gender,
          locale: @data.extra.raw_info.locale,
          password: Devise.friendly_token[0,20]
        )
        @user.skip_confirmation! if @data.info.verified
        @user.save!
      end

      # Associate the identity with the user if needed
      if identity.user != @user
        identity.user = @user
        identity.profile = @data.info.urls.Facebook
        identity.token = @data.credentials.token
        identity.save!
      end

      return @user
    end
  end

  # [Role] Product
  class GoogleUser
    def initialize(identity, data)
      @identity = identity
      @data = data
    end

    def create
      @user = ::User.find_by(email: @data.info.email)

      # Create the user if it's a new registration
      if @user.blank?
        @user = ::User.new(
          first_name: @data.info.first_name,
          last_name: @data.info.last_name,
          email: @data.info.email,
          image: @data.info.image,
          gender: @data.extra.raw_info.gender,
          locale: @data.extra.raw_info.locale,
          password: Devise.friendly_token[0,20]
        )
        @user.skip_confirmation! if @data.extra.raw_info.email_verified
        @user.save!
      end
      
      # Associate the identity with the user if needed
      if @identity.user != @user
        @identity.user = @user
        @identity.profile = @data.extra.raw_info.profile
        @identity.token = @data.credentials.token
        @identity.save!
      end

      return @user
    end
  end
end