title: Reliable technique for tracking invitations to mobile installations
body: <p>We allow our existing mobile app users to invite their friends via email, text message, or Facebook request.   We can track the "accepted" invitations as long as the invited user signs up the same way they were invited (ie by the same email, phone number, or Facebook).  Otherwise they go untracked. </p>
  
  <p>We know there's a reliable way to identify a device at the time the invited user taps the link (in the email, text message invitation), and then once the app is installed, recognize the device as the same one, and make the match. We've seen an app that pulls it off.</p>
  
  <p>We need a solution for both iOS and Android.  And the big challenge is both platforms sandbox the webView, so no cookie left when the invitation link was originally tapped is detectable from a webview from within the newly-installed app. And, we don't want to compromise the user experience with any kind of app-swap gyration of launching the browser, then having it re-launch our app.</p>
  
  <p>None of the techniques we've explored seem to be ideal.  We've looked into: matching caller IP addresses (within in a smallish time window); browser "fingerprinting"; a clipboard copy/paste scheme; et.al.  Further, none of these approaches seem to be what's being used by the aforementioned app with the special magic :)</p>