rack_openid_example.rb

require 'sinatra'
require 'haml'
# Session needs to be before Rack::OpenID
use Rack::Session::Cookie

require 'rack/openid'
require 'gapps_openid'

use Rack::OpenID

get '/login' do
  haml :login
end

post '/login' do
  if resp = request.env["rack.openid.response"]
    p resp.class
    if resp.status == :success
      ax_response = OpenID::AX::FetchResponse.from_success_response(resp)
      @email = ax_response['http://axschema.org/contact/email'].first
      "Welcome: #{@email}"
    else
      "Error: #{resp.status}"
    end
  else
    headers 'WWW-Authenticate' => Rack::OpenID.build_header(
      :identifier => "http://randomgoogleappdomain.org",
      :required => ['http://axschema.org/namePerson/friendly', 'http://axschema.org/contact/email']
    )
    throw :halt, [401, 'got openid?']
  end
end

enable :inline_templates

__END__

@@ login

You need to sign in with your randomgoogleappdomain.org account
%form{:method => "post", :action => '/login'}
	%input{:type => 'submit', :value => "proceed to login"}

Gemfile:
gem "sinatra"
gem "shotgun"
gem "haml"
gem "ruby-openid"
gem "ruby-openid-apps-discovery"
gem "rack-openid"