There was a discussion some time ago about mitmproxy (a tool similar to Charles) and specifically about certificate pinning / iOS apps. See here[0]

It seems like you need a jailbroken device, and that there are tools such as SSL Kill Switch[1]

[0] https://news.ycombinator.com/item?id=15757878 [1] https://github.com/iSECPartners/ios-ssl-kill-switch