Fun with your friend's Facebook and Tinder sessions
I'm trying to think about whether there's a way for Facebook and/or Tinder to mitigate this attack without degrading user experience. Because the auth token used is from the response to the last request ever made from Steve's computer, having a changing auth token on each request wouldn't help in this scenario. Restricting an auth token to an IP address wouldn't work since both users are presumably behind the same NAT (all devices on the same residential WiFi router) - not to mention that IP addresses change all the time. Restricting an auth token to a user agent string would stop the first attempt at this hack - but then someone would simply tell the proxy to mimic the UA of Steve's desktop - but then could Facebook refuse to honor mobile application authorization requests if the mobile device is mimicking a desktop browser's UA?