TOTP(Time-based One-Time Password)
A six-to-eight digit code that changes every 30 seconds, used as a second authentication factor.
TOTP is what apps like Aegis, Authy or Google Authenticator generate. Enabling TOTP-based two-factor authentication on your self-hosted services dramatically reduces the risk from stolen or reused passwords.
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2FA / MFA(Two-Factor / Multi-Factor Authentication)
Requiring more than just a password to log in — typically something you know plus something you have.
SSO(Single Sign-On)
Logging in once with a central identity provider to access many separate applications.