The new ATS involved by iOS 9 cause lots of http related functionalities stop working. I have to add all the http request url into a whitelist or I could simply disable the
All connections using the NSURLConnection, CFURL, or NSURLSession APIs use App Transport Security default behavior in apps built for iOS 9.0 or later, and OS X 10.11 or later. Connections that do not follow the requirements will fail.
However, You can specify exceptions to the default behavior in the Info.plist file in your app or extension. Use the keys in the property list for specific exceptions or to turn off App Transport Security. Table 1-1 shows the keys and their types, and uses indentation to indicate structure.
Here is the source link: https://developer.apple.com/library/prerelease/ios/technotes/App-Transport-Security-Technote/index.html