xcconfig files

The two main config files are Debug.xcconfig and Release.xcconfig. Both include Shared.xcconfig, which includes Local.config. The local file is in .gitignore so you need to create an empty one if you don't want warnings about the file being missing.

Therefore the local config file can be used to supply settings that shouldn't be included in git, like API keys and secrets. Here is the one I'm (@mlilback) is using:

INFOPLIST_PREPROCESS = YES
INFOPLIST_PREPROCESSOR_DEFINITIONS=LSERVER_UPDATE_URL='http://www.rc2.io/imageInfo.json' \ 
SPARKLE_FEED_URL='https://rink.hockeyapp.net/api/2/apps/7574682489924a239272b421546d00f8'

OTHER_SWIFT_FLAGS = $(inherited) -DHOCKEYAPP_ENABLED 
GCC_PREPROCESSOR_DEFINITIONS = $(inherited) HOCKEYAPP_ENABLED=1 HOCKEY_IDENTIFIER='@"<PRIVATE DATA>"'

DEVELOPMENT_TEAM = <PRIVATE DATA>

The INFO_PLIST (especially LSERVER_UPDATE_URL) and DEVELOPMENT_TEAM are the essential ones.