google_oauth2.rb

require 'rubygems'
require 'bundler'
Bundler.setup :default, :development, :example
require 'sinatra'
require 'omniauth'
require 'omniauth-google-oauth2'
use Rack::Session::Cookie
use OmniAuth::Builder do
  provider :google_oauth2, ENV['GOOGLE_KEY'], ENV['GOOGLE_SECRET'], {
    :scope => 'https://www.googleapis.com/auth/plus.me https://www.googleapis.com/auth/plus.stream.read https://www.googleapis.com/auth/plus.stream.write https://www.googleapis.com/auth/plus.circles.read https://www.googleapis.com/auth/plus.circles.write'
  }
end
get '/' do
  <<-HTML
  <ul>
    <li><a href='/auth/google_oauth2'>Sign in with Google</a></li>
  </ul>
  HTML
end
get '/auth/:provider/callback' do
  content_type 'text/plain'
  request.env['omniauth.auth'].info.to_hash.inspect
end