title: Register User via SMS in Google App Engine
body: <p>I am setting up an App Engine application, and I want to register all my users based on their phone number (like Whatsapp).</p>
  
  <p>The server will need to send an SMS to the user to authenticate. Then the user can log in with a combination of their phone number + password.</p>
  
  <p>Does Google Apps support this type of authentication model, or do I have to use a Google Account? </p>
  
  <p>I saw Twilio support, but that seems more for setting up an app that sends a bunch of SMSes/VoIP server side.  I just need to receive one SMS per user to confirm their phone number.</p>
  
  <p>Note: this will be a iOS/Android app, with possible web support in the future.</p>