Macbook Air how to setup proxy for iTunes and App Store? I am confused how to setup proxy for iTunes and App Store on Macbook Air.

I have noticed that Safari can connect to the Internet through proxy, but for iTunes and App Store, I do not know how it works. 

Can you help me with this? Thanks.
The Change Settings… button in Safari > Preferences… > Advanced opens the global Proxies sheet. Changes made here affect every app that uses that connection.





Alternatively the sheet can be opened by opening System Preferences.app, selecting Network, then Advanced…, then Proxies.