Which statement correctly describes single sign-on (SSO)?

Answer: A. A mechanism that lets one authentication give access to multiple linked services without logging in again; it improves convenience, but because a breach of that authentication affects many services, it should preferably be combined with multi-factor authentication

With single sign-on (SSO), once a user logs in to the system that performs authentication (the IdP, or identity provider), the result is passed securely to each linked service, so the user can use them without logging in again for each one. Typical protocols are SAML and OpenID Connect. Because passwords are not handed to each service, there are fewer passwords to manage, and there are administrative benefits too, such as being able to disable a departing employee's account in one place. However, if the IdP account is taken over, the attacker gets into every linked service, so multi-factor authentication at the IdP is especially important. Password reuse is something else entirely: it lets a password leaked from one service be used to get into others (credential stuffing).

• A. Correct. One authentication gives access to multiple services, but because a breach has a large impact, it is combined with multi-factor authentication.
• B. Password reuse is a dangerous practice in which a leak in one place lets attackers into other services; it is not SSO.
• C. Limiting how many people can log in at once has nothing to do with SSO.