Simple module for doing Oauth with google.

authable.rb

module Authable
  extend ActiveSupport::Concern
  OAUTH_CLIENT_ID     = '123.apps.googleusercontent.com'
  OAUTH_CLIENT_SECRET = '456'
  OAUTH_BASE_URL      = 'https://www.googleapis.com/oauth2/'
  OAUTH_SCOPE         = ['https://www.googleapis.com/auth/userinfo.email',
                         'https://www.googleapis.com/auth/userinfo.profile']

  module ClassMethods
    def google_oauth_url(callback_url)
      params = {
        response_type: 'code',
        client_id:     OAUTH_CLIENT_ID,
        scope:         OAUTH_SCOPE.join('+'),
        redirect_uri:  callback_url
      }

      'https://accounts.google.com/o/oauth2/auth?' +
        params.to_query.gsub('%2B','+') # google expects the + unescaped
    end

    def get_users_details(code, callback_url)
      access_token = get_access_token(code,callback_url)
      uri          = URI.parse "#{OAUTH_BASE_URL}v1/userinfo?access_token=#{access_token}"
      http         = Net::HTTP.new(uri.host, uri.port)
      http.use_ssl = true
      request      = Net::HTTP::Get.new(uri.request_uri)

      response = http.request(request)
      JSON.parse(response.body)
    end

    private
    def get_access_token(code, callback_url)
      uri          = URI.parse "#{OAUTH_BASE_URL}/token"
      http         = Net::HTTP.new(uri.host, uri.port)
      http.use_ssl = true
      request      = Net::HTTP::Post.new(uri.request_uri, {'Content-Type' => 'application/x-www-form-urlencoded'})
      request.body = {
        code:          code,
        grant_type:    'authorization_code',
        client_id:     OAUTH_CLIENT_ID,
        client_secret: OAUTH_CLIENT_SECRET,
        redirect_uri:  callback_url
      }.to_query

      response = http.request(request)
      JSON.parse(response.body)['access_token']
    end
  end
end