What is Sign in with Apple?
Day One now uses Sign in with Apple to sign into a Day One Sync account. This is a new feature provided by Apple to sign into accounts or services without having to create a unique login.
Data is still synced to Day One Sync, but this feature simplifies the sign-in process for users and offers security and privacy. Sign in with Apple requires iOS 13 or later.
Details about this feature, including how to manager your information with Sign in with Apple can be found on Apple's website here.
When you see a Sign in with Apple button on a participating app or website, it means you can set up an account and sign in with your Apple ID. Instead of using a social media account, or filling out forms and choosing another new password, just tap the Sign in with Apple button, review your information, and sign in quickly and securely with Face ID, Touch ID, or your device passcode.
Sign in with Apple is built from the ground up to respect your privacy and keep you in control of your personal information. At your first sign in, Day One can ask only for your name and email address to set up an account for you. You can use Hide My Email—Apple's private email relay service—to create and share a unique, random email address that forwards to your personal email. That way you can receive useful messages from us without sharing your personal email address. Only the registered app or site developer can communicate with you using this email, and you can turn it off at any time.
Sign in with Apple won’t track or profile you as you use your favorite apps and websites, and Apple retains only the information that’s needed to make sure you can sign in and manage your account.
Update from Cloudkit
Previously, the option to sign in with Apple ID used an older system from Apple called CloudKit. This used the Apple ID credentials from the iCloud settings on the device. See more here. Users that have linked their Apple ID to their Day One account can update to the new Sign in with Apple in Day One > Settings > Tap the name at the top > Update on the line for Sign in with Apple.