title: How does Whatsapp Authentication work?
body: <p>I want to develop a mobile app and use a whatsapp like user registration. Now I remember the security problems that were discussed some years ago. Whatsapp used to authenticate users simply by their phone number and IMEI. Now of course this is not really safe but I don't really know how to do it more secure.</p>
  
  <p>Now I didn't hear something  about Whatsapp authentication problems anymore for a long time so I guess they have  secure method now. Do you know how Whatsapp does it today?</p>