I like to intercept iOS apps' traffic with Burp Suite[1] or Fiddler[2]. The trick is to have two adapters running on the same OS, one for the public Internet, and the other acting as an ad-hoc hotspot. It's simply a case of letting Burp suite sniff the traffic on the ad-hoc network and seeing what 'goodies' you find, like API keys.

[1]: https://portswigger.net/BURP/

[2]: http://www.telerik.com/fiddler