title: Mobile app: how to show the OTP my app sends in a popup without leaving my app?
body: <p>We've had to code an OTP based authentication. I have seen some apps, like my bank's app, which when it sends the OTP also then immediately does a quick popup of the SMS that has just arrived, so I can see the OTP <em>without</em> leaving the app. I just memorize the number, close the popup, and get on with the login inside that app. </p>
  
  <p>How do they do that? Is there some iOS/Android spec I should be looking at, which allows us to similarly popup the OTP without the user having to go to the SMS screen, then come back to our app? Thanks! </p>
  
  <p>EDIT: I have very useful Android suggestions. Now looking for iOS variations of these recommendations. Understand iOS has much more stringent sandboxing limitations, so the "listener" may be more complex? </p>