Researcher Bhavuk Jain in April
discovered a critical Sign in With Apple vulnerability that could have resulted in a takeover of some user accounts. The bug was specific to third party apps that used Sign in With Apple and didn't implement additional security measures.
Jain notes that Sign in With Apple works by authenticating a user through a JWT (JSON Web Token) or a code that's generated by Apple's server. Apple then gives users the option to share either the email tied to their Apple ID or a private relay email address,which creates a JWT that's used to login a user.
