Building a Rails based app for Google Apps Marketplace

Editor's note: This is a guest post by Benjamin Coe. Benjamin shares tips and best practices on using Ruby on Rails for integrating with Google Apps and launching on the Marketplace. — Arun Nagarajan

Yesware offers an app in the Google Apps Marketplace which allows our users to schedule reminders, from directly within the Gmail UI. Yesware’s app recently relaunched in the updated Google Apps Marketplace. In prep, we revamped our existing Google Apps Integration:
  • Replacing OpenID with OAuth 2.0 for Single-Sign-On.
  • Replacing 2-legged OAuth with OAuth 2.0 Service Accounts, for delegated account access.
  • Releasing a Gmail Contextual Gadget that worked within these new authentication paradigms.
We should like to share some of the decisions we made, and challenges we faced, upgrading our production Ruby on Rails application to support the improved Google Apps Marketplace.

OAuth 2.0 for SSO

In the revamped Google Apps Marketplace, OAuth 2.0 replaces OpenID for facilitating Single-Sign-On. The flow is as follows:

  1. OAuth 2.0 credentials are created in the Cloud Console, within the same project that has the Google Apps Marketplace SDK enabled.
  2. When accessing your application, a user is put through the standard OAuth 2.0 authentication flow using these credentials.
  3. If the user has the Google Apps Marketplace App installed they will be logged directly into your application, skipping the authorization step.
To implement the OAuth 2.0 authentication flow, you can use the OmniAuth Google OAuth2 Strategy gem. Assuming you're already using OmniAuth, you simply add a line to initializers/omniauth.rb that looks something like this: 
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :google_oauth2, ENV["GAM_OAUTH_KEY"], ENV["GAM_OAUTH_SECRET"]
end

Yesware already had a Google OAuth 2.0 authentication strategy, so we opted to subclass the Google OAuth 2.0 OmniAuth Strategy. This allowed us to continue supporting our existing OAuth 2.0 credentials, while adding support for Google Apps Marketplace SSO. Our subclassed strategy looked like this: 
# Subclass the GoogleOauth2 Omniauth strategy for
# Google Apps Marketplace V2 SSO.
module OmniAuth
  module Strategies
    class GoogleAppsMarketplace < OmniAuth::Strategies::GoogleOauth2
      option :name, 'google_apps_marketplace'
    end
  end
end
Our final initializers/omniauth.rb file was this:
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :google_oauth2,  ENV["OAUTH_KEY"], 
                            ENV["OAUTH_SECRET"], 
                            {:scope => ENV["OAUTH_SCOPE"]}
  provider :google_apps_marketplace,  ENV["GAM_OAUTH_KEY"],  
                                      ENV["GAM_OAUTH_SECRET"], 
                                      { :scope => ENV["GAM_OAUTH_SCOPE"], 
                                        :access_type => 'online' }end

Note that :access_type is set to online. This is necessary to prevent the authorization prompt from being presented to a SSO user. Omniauth defaults to an :access_type of offline.
That's all it takes. With this OmniAuth strategy in place, when a domain administrator installs your application SSO will be available across the domain.

OAuth 2.0 Service Accounts

To support Yesware's reminder functionality, we needed offline access to a user's email account. In the past, this functionality was supported through 2-legged OAuth. In the new Google Apps Marketplace paradigm, OAuth 2.0 Service Accounts are the replacement.
  • In the Cloud Console, generate a private key for the OAuth 2.0 Service Account associated with your Google Apps Marketplace project. 
  • Download the .p12 private key generated. 
  • Place this key somewhere that will be accessible by your production servers, e.g., a certificates folder in your codebase. 
We used the Google API Ruby Client gem to generate an access token from our Service Account's keys.
Using the deprecated 2-Legged OAuth based approach, our authorization logic looked like this:

Gmail.connect!(:xoauth, '[email protected]', {
  token: authentication.token,
  secret: authentication.secret,
  consumer_key: google.key,
  consumer_secret: google.secret,
  read_only: true
})
Using the new Service Account Based Approach, it was as follows: 
key = Google::APIClient::PKCS12.load_key(
google_apps.service.p12path, # this is a constant value Google uses
# to password protect the key.
'notasecret'
)service_account = Google::APIClient::JWTAsserter.new(
google_apps.service.email,
'https://mail.google.com/',
key
)client = Google::APIClient.new(
:application_name => APPLICATION_NAME,
:version => APPLICATION_VERSION
).tap do |client|
client.authorization = service_account.authorize('[email protected]')end
Google.connect!(:xoauth2, '[email protected]', {
:oauth2_token => client.authorization.access_token,
})
With OAuth 2.0 Service Accounts, the underlying libraries we used to interact with Gmail remained the same. There were simply a few extra steps necessary to obtain an access token.

Contextual Gadgets and SSO

Yesware provides a Gmail Contextual Gadget, for scheduling email reminders. To facilitate this, it's necessary that the gadget interact with a user's email account. To make this a reality, we needed to implement SSO through our contextual gadget. Google provides great reading material on this topic. However, the approach outlined concentrates on the deprecated OpenID-based SSO approach. We used a slightly modified approach.
Rather than OpenID, we used OAuth 2.0 for associating the opensocial_viewer_id with a user. To do this, we needed to modify our OmniAuth strategy to store the opensocial_viewer_id during authentication:
# Subclass the GoogleOauth2 Omniauth strategy for
# Google Apps Marketplace V2 SSO.
module OmniAuth
  module Strategies
    class GoogleAppsMarketplace < OmniAuth::Strategies::GoogleOauth2

      option :name, 'google_apps_marketplace'

      def request_phase

        # Store the opensocial_viewer_id in the session.
        # this allows us to bind the Google Apps contextual
        # gadget to a user account.
        if request.params['opensocial_viewer_id']
          session[:opensocial_viewer_id] = request.params['opensocial_viewer_id']
        end

        super
      end

    end
  end
end
Once an opensocial_viewer_id was connected to a Yesware user, we could securely make API calls from our contextual gadget. To cut down on the ritual surrounding this, we wrote a Devise Google Apps OpenSocial Strategy for authenticating the OpenSocal signed requests.

Now Go Forth

Once we figured out all the moving parts, we were able to use mostly off the shelf mature libraries for building our Google Apps Marketplace Integration. I hope that this retrospective look at our development process helps other Rails developers hit the ground running even faster than we did.
Benjamin Coe profile

Benjamin Coe cofounded the email productivity company Attachments.me, which was acquired by Yesware, Inc., in  2013. Before starting his own company, Ben was an engineer at FreshBooks, the  world’s #1 accounting solution.
Ben’s in his element when writing scalable cloud-based infrastructure, and loves reflecting on the thought-process that goes into this. A rock-climber, amateur musician, and bagel aficionado, Ben can be found roaming the streets of San Francisco.
[email protected] — https://github.com/bcoe— @benjamincoe