Single Sign-On (SSO) is a critical authentication mechanism that allows users to sign in once and access multiple applications without the requirement to re-enter credentials. This enhances user experience, prevents password fatigue, and eliminates security threats posed by weak or duplicated passwords. SSO is connected to identity providers (IdPs) through protocols such as SAML, OAuth, or OpenID Connect to securely authenticate users. It improves regulatory compliance by consolidating authentication and access control. Yet, an ill-designed SSO system can be a single point of failure, so redundancy, multi-factor authentication (MFA), and ongoing monitoring are essential to provide security and availability.