The block to execute when this
CKFetch object fetches the web authentication token.
- iOS 9.2+
- macOS 10.11.2+
- Mac Catalyst 13.0+
- tvOS 9.1+
- watchOS 3.0+
The block returns no value and takes the following parameters:
If the operation is successful, the web authentication token; otherwise,
An error object containing information about a problem, or
The operation object executes this block only once and it is your only chance to process the operation results. Your block must be capable of executing on a background thread, so any tasks that require access to the main thread must be redirected accordingly.