Twitter app on iOS 9 doesn’t connect through proxy

First, this is a really good question. Wow. I've been trying for days to figure out how to attack this one.

I set up "Charles Web Debugging Proxy" on my Mac and set up my iPhone to hit it.

First, it hits http://api.facebook.com/restserver.php, which spits this back:

<chat_connect_response xmlns="http://api.facebook.com/1.0/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://api.facebook.com/1.0/ http://api.facebook.com/1.0/facebook.xsd"> 
<host>9.channel</host> 
<port>80</port> 
<channel>p_123456789</channel> 
<seq>0</seq> 

Meanwhile, it also connects to iphone.facebook.com which gives some XML. Then it connects to 0.9_channel.facebook.com:80 and sends some requests which return JSON.

It looks like everything is done over port 80. Are you sure theres no other problem on your end?

Enable web sharing and place the PAC file (e.g. proxy.pac) in the documents folder (/Library/WebServer/Documents). Then set the auto proxy setting to http://127.0.0.1/proxy.pac. If the changes don't take effect immediately or you change the contents of the PAC file at any point in time you need to restart Safari and clear its cache. If this doesn't help, reboot the system.