A good way to create the authentication for Facebook

user.rb

def apply_omniauth(omniauth, save_it = false)
    case omniauth['provider']
    when 'facebook'
      self.apply_facebook(omniauth)
    end
    self.email = omniauth['user_info']['email'] if email.blank?
    build_authentications(omniauth, save_it)
  end
  
  def build_authentications(omniauth, save_it = false)
    auth_params = {:provider => omniauth['provider'], :uid => omniauth['uid'], :token =>(omniauth['credentials']['token'] rescue nil)}
    if save_it
      authentications.create!(auth_params)
    else
      authentications.build(auth_params)
    end
  end
  
  def apply_omniauth!(omniauth)
    apply_omniauth(omniauth, true)
  end