How do I set up two-factor authentication (2FA)?

Two-factor authentication adds a 6-digit code (from an authenticator app) on top of the password. To enable it: go to your Profile, open the two-factor setup, and scan the QR code with an app like Google Authenticator or Authy. Enter the code it shows to confirm, and save your recovery codes somewhere safe. From then on, signing in asks for your password and then the current 6-digit code. If you lose your device, use a recovery code. Owners should enable 2FA on all high-privilege accounts.