Get a user's google contacts using their valid access token (so they only need to authenticate once)

google_contact_list

require "net/http"
require "rexml/document"

class GoogleContactList
  
  attr_reader :token
  attr_accessor :response

  class << self
    def cache
      @cache ||= Hash.new
    end

    def for(token)
      cache[token] || new(token).contacts
    end
  end

  def cache(data)
    self.class.cache[token] = data
  end

  def initialize(token)
    @token = token
  end

  def get
    http.use_ssl = true
    http.verify_mode = OpenSSL::SSL::VERIFY_NONE
    self.response = http.get(path, headers)
  end

  def emails
    contacts.collect{|contact| contact[:email]}
  end

  def document
    @document ||= REXML::Document.new get.body
  end

  def contacts
    @contacts ||= cache(document.elements.collect('//entry') do |entry|
      gd_email = entry.elements['gd:email']
      {
        name: entry.elements['title'].text,
        email: (gd_email.attributes['address'] if gd_email)
      }
    end)
  end

  private
  def self.uri
    @uri ||= URI.parse('https://www.google.com')
  end

  def self.http
    @http ||= Net::HTTP.new(uri.host, uri.port)
  end

  def http
    self.class.http
  end

  def headers
    {
      'Authorization' => "AuthSub token=#{token}",
      'GData-Version' => '3.0'
    }
  end

  def path
    @path ||= '/m8/feeds/contacts/default/full'
  end
end

I've used it in a devise omniauth controller, to populate a list of contacts in session:

class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
  def google_oauth2
    # You need to implement the method below in your model (e.g. app/models/user.rb)
    @user = User.find_for_google_oauth2(request.env["omniauth.auth"], current_user)
    logger.info request.env["omniauth.auth"].inspect
    if !@user
      flash[:notice] = 'You are not able to log into this resource'
      redirect_to new_user_session_path
    elsif @user.persisted?
      flash[:notice] = I18n.t "devise.omniauth_callbacks.success", :kind => "Google"
      token = request.env["omniauth.auth"].credentials.token
      session['contacts'] = GoogleContactList.for(token)
      sign_in_and_redirect @user, :event => :authentication
    else
      session["devise.google_data"] = request.env["omniauth.auth"]
      redirect_to new_user_registration_url
    end
  end
end

However, the list of contacts seems fairly random. I think what I actually need is most used contacts which I think I need to access via the google + api and not the google contacts api used here.