Gigya's iOS SDK fully supports iOS 9.
Facebook SDK v4.7.1 - https://developers.facebook.com/docs/ios.
Google+ SDK v1.7.1 - https://developers.google.com/+/mobile/ios/getting-started.
The temporary flag 'NSAllowsArbitraryLoads' will disable 'App Transport Security' globally in your app if it is not prepared for migration. For more information, see https://forums.developer.apple.com/thread/3544.
Facebook's default login behavior 'FBSDKLoginBehaviorNative' has been changed on iOS 9 to login via WebView, even if the Facebook app is installed. This is by design.
For more information, see https://developers.facebook.com/bugs/786729821439894/?search_id.
There is currently an open issue with Facebook: "...the first app switch for a given scheme will also prompt the user with a confirmation dialog. We are investigating this but there is no workaround at this time."
For more information, see https://developers.facebook.com/docs/ios/ios9#whitelistapp.