app.rb

require 'rubygems'
require 'bundler/setup'
require 'sinatra'
require 'omniauth'
require 'openid/store/filesystem'

use Rack::Session::Cookie

use OmniAuth::Builder do
  provider :open_id, OpenID::Store::Filesystem.new('/tmp')
  provider :twitter, 'xxx', 'xxx'
end

enable :static

get '/' do
  if @auth
      "Welcome #{@auth.inspect} "
  else
      "Logged out. <a href='/auth/twitter'>login</a>"
  end
end

get '/auth/:provider/callback' do
  @auth = request.env['omniauth.auth']
  @auth.inspect
end