Authenticator Assurance Level (AAL) is the measure of the strength of an authentication mechanism.
In Supabase, having an AAL of aal1 refers to having the 1st factor of authentication such as an email and password or OAuth sign-in while aal2 refers to the 2nd factor of authentication such as a time-based, one-time-password (TOTP).
If the user has a verified factor, the next_level field will return aal2, else, it will return aal1.