user_session.rb

class UserSession < Authlogic::Session::Base
  def self.twitter_consumer
    @twitter_consumer ||= OAuth::Consumer.new(
      TwitterOAuthConsumerKey,
      TwitterOAuthSecretKey,
      :site => "http://twitter.com"
    )
  end
  
  def authorize_via_twitter
    controller.redirect_to request_token.authorize_url
  end
  
  def request_token
    @request_token ||= load_request_token || create_request_token
  end

  def create_request_token
    token = self.class.twitter_consumer.get_request_token
    dump_request_token token
    token
  end
  
  def dump_request_token token
    self.raw_request_token = token.to_yaml
  end
  
  def load_request_token
    return nil unless raw_request_token
    YAML.load raw_request_token
  end
  
  def raw_request_token
    controller.session[:twitter_request_token]
  end
  
  def raw_request_token= token
    controller.session[:twitter_request_token] = token
  end
  
  def oauth_tokens_match?
    controller.params[:oauth_token] == request_token.token  
  end
  
  def connecting_through_twitter?
    @connecting_through_twitter ||= !!raw_request_token
  end
  
  def connected_through_twitter?
    @connected_through_twitter ||= !!twitter_credentials
  end
  
  def twitter_credentials
    controller.session[:twitter_credentials] ||= JSON.parse(access_token.get('/account/verify_credentials.json').read_body)
  end
  
  def access_token
    @access_token ||= request_token.get_access_token
  end
  
  def purge_request_token!
    @access_token               = nil
    @request_token              = nil
    @connecting_through_twitter = nil
    @connected_through_twitter  = nil
    self.raw_request_token = nil
  end
  
  def twitter_auth_error!
    errors.add_to_base("
      We have had an honest misunderstanding with Twitter.
      The Web is a big place, sometimes we get confused and lost along the way.
      Please try connecting through Twitter again.")
  end
  
  def save
    if connecting_through_twitter?
      unless oauth_tokens_match? && connected_through_twitter?
        twitter_auth_error!
        yield false
        return
      end

      record = klass.for_twitter_credentials(twitter_credentials)

      if !record
        purge_request_token!
        twitter_auth_error!
        yield false
        return
      end

      self.unauthorized_record = record
      result = super
      save_cookie
      return result
    else
      super
    end
  rescue OAuth::Unauthorized
    purge_request_token!
    twitter_auth_error!
    yield false
    return
  end
  
  def authentication_method
    connected_through_twitter? ? 'twitter' : 'password'    
  end
end