Facebook for developers – Custom Audiences

"Custom Audiences from CRM Data

Build the target Custom Audiences from customer information. This includes email addresses, phone numbers, names, dates of birth, gender, locations, App User IDs, Page Scoped User IDs, Apple's Advertising Identifier (IDFA), or Android Advertising ID."

How and where does one get Apple's and Google/Android's Advertising ID? This rings quite different to Apple's current privacy stance of preventing tracking in upcoming iOS and macOS releases.