example code for doing OAuth with Twitter using the oauth gem.

some_auth_controller.rb

def SomeAuthController < ApplicationController

  def twitter_auth
    request_token = twitter_consumer.get_request_token(:oauth_callback => twitter_callback_credentials_url)
    session['twitter_request_token'] = request_token.token
    session['twitter_request_secret'] = request_token.secret
    redirect_to request_token.authorize_url
  end

  def twitter_callback
    request_token = OAuth::RequestToken.new(twitter_consumer, session['twitter_request_token'], session['twitter_request_secret'])
    access_token = request_token.get_access_token(:oauth_verifier => params[:oauth_verifier])
    # ...
  end

  private
    def twitter_consumer
      @oauth_consumer ||= OAuth::Consumer.new(CONSUMER_KEY, CONSUMER_SECRET, :site => 'http://api.twitter.com', :request_endpoint => 'http://api.twitter.com', :sign_in => true)
    end

end