From bhavukjain.com
What if I say, your Email ID is all I need to takeover your account on your favorite website or an app. Sounds scary, right? This is what a bug in Sign in with Apple allowed me to do.
In the month of April, I found a zero-day in Sign in with Apple that affected third-party applications which were using it and didn’t implement their own additional security measures. This bug could have resulted in a full account takeover of user accounts on that third party application irrespective of a victim having a valid Apple ID or not.