twitter-login.rb

require 'rubygems'
require 'sinatra'
require 'twitter/login'
require 'haml'

use Rack::Session::Cookie
use Twitter::Login, 
    consumer_key: "__YOUR_KEY_HERE__",
    secret:       "__YOUR_SECRET_HERE__",
    return_to:    "/authenticated"

helpers Twitter::Login::Helpers

get "/" do
  haml :home
end

get "/authenticated" do
  @user = twitter_user

  haml :user
end

__END__

@@home
%h1 Hello world
%a(href='/login') Login to Twitter

@@user
%h1 Welcome #{@user.name}

%dl
  %dt Screen Name:
  %dd= @user.screen_name

  %dt Twitter ID:
  %dd= @user.id