Nintendo has secretly added two factor authentication (TFA) functionality to all Nintendo Accounts worldwide.
A Nintendo Account is used to purchase games on your Nintendo Switch, play online, and connect to smartphone apps developed by Nintendo.
When TFA is activated on your Nintendo Account, besides requiring a password to login to your account, a code will be sent to Google Authenticator to verify that it’s indeed you. Entering the correct code will grant you access to your account.
To activate TFA, simply head over to the official Nintendo Account website, login, click “Sign-in and security settings”, and click “Edit” on 2-Step Verification Settings. From there you can set up TFA on your account.