On September 19, 2017, Apple released iOS11 and with it, Safari’s new Intelligent Tracking Prevention (ITP). ITP limits the use of 3rd party cookies to 24 hours and deletes a site's cookies entirely for sites not visited within a 30-day period. This will affect developers who use Facebook Social Plugins, Facebook Analytics and Facebook Login.
So what does this actually mean?
Safari will delete facebook.com cookies for people who haven't visited facebook.com in the last 30 days.
For Facebook Social Plugins: Users interacting with facebook.com within the last 24 hours will be able to use Social Plugins normally on the sites they visit. Anyone using Safari who does not visit facebook.com on a daily basis will be required to go through an additional confirmation screen in order to use Facebook's Social Plugins such as Like, Comment or Share. Those who don't visit facebook.com for more than 30 days in Safari may have to re-login with their username and password in order to use these features or use Facebook Login.
For Facebook Analytics: Businesses and developers using Facebook Analytics may see higher unique user counts reported for people visiting their mobile website on an iOS device.
For Facebook Login: Additionally, Apple has made changes in iOS that isolate apps from the main Safari browser. This can mean that people using Facebook Login may have to enter their username and password every time they use Facebook Login with an app, instead of just once per device.
To mitigate the impact of ITP, apps using Facebook Login should update to our latest SDK and use the SFAuthenticationSession API. This allows cookie sharing after users agree to an interstitial dialog from iOS.
We're working on a solution for Facebook Social Plugins that will require people to go through an additional login screen more often on Safari. We're also actively working with Apple to make this an easy transition for everyone and will keep you informed of future developments.