How to use the Microsoft Authenticator WP app with Google
But a little know fact is that this app can also be used for the Google Account Two-factor authentication. See the screenshots below on how to do this:
Go to the right corner of you Google page and select Account.
On the left you will see some options, select Security.
When you haven’t entered a mobile phone number, you’ll have to do it now. Be sure it can receive SMS.
After requesting a code and receiving it, enter it and verify.
Optionally, you can let Google trust the current computer you are working on. This is not necessary for our goal.
Confirm enabling 2-step verification.
Now 2-step verification is configured, but not yet enabled. In the middle you can see the option for Mobile Application with the options: Android, iPhone and Blackberry. No Windows Phone. However, just choose Android.
A QR code appears. Start your Windows Phone Authenticator app, add an account (with the plus). It will request an account name and secret key, but you can scan the QR code by pressing the camera icon within the app (not the physical button on your WP phone). Enter the code which appears within the app for you Google account.
You’ll get a confirmation.
And now 2-step verification is active and works with the Windows Phone app. No need for Android, iPhone or Blackberry!
Be safe! Or in Dutch: “Hou je veilig!”
Update: The reverse is also true. You can use the Google Authenticator app for Microsoft Accounts. It's available for Android, iOS and Blackberry. Thanks to The UC Architects fellow and Exchange MVP Mahmoud Magdy for confirmation.
And if you have multiple devices, let each of them scan the same QR code. That way they each show the same code. However, you could consider this a bit less save (more devices to lose).