# app/policies/twitter_policy.rb
class TwitterPolicy < Struct.new(:auth)

  def first_name
    auth['info']['name'].split(' ').first
  end

  def last_name
   .....
  end

  ....
end


# app/policies/facebook_policy.rb
class FacebookPolicy < Struct.new(:auth)
  def first_name
    auth['info']['name'].split(' ').first
  end

  def last_name
   .....
  end

  ....
end

# app/models/user.rb
def self.from_oauth(auth)  
  policy = "#{auth['provider']}_policy".classify.constantize.new(auth)
  create_user_from_policy(policy)
end

# check https://github.com/elabs/pundit for maximum usage of policies