# What is Single Sign-On (SSO)?

> Single sign-on (SSO) is an authentication process in which one account and its authenticators let a user access multiple applications without performing a full sign-in separately at each one.

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## Content

Common implementations use an identity provider that authenticates the user and sends protected assertions or tokens to applications that trust it.

SSO can reduce password exposure and user friction while centralizing authentication policy, MFA, session controls, logging, and account disablement. Each application must still make its own authorization decisions: successful SSO establishes or conveys identity and authentication context, but it does not mean the user should receive the same permissions everywhere.

### Key points

- **Trust design:** Define which identity providers, applications, signing keys, redirect locations, attributes, and assurance signals are trusted.
- **Lifecycle value:** Central provisioning and deprovisioning can make access changes faster, provided application accounts and sessions are actually removed or revoked.
- **Session security:** Protect identity-provider and application sessions against theft, fixation, replay, excessive duration, and unsafe recovery.
- **Resilience:** Plan for identity-provider outages, key rollover, configuration errors, compromised administrators, emergency access, and controlled fallback.
- **Important limitation:** SSO concentrates dependency and privilege. Compromise of an identity provider, federation configuration, or active session can affect many applications at once.

### Related terms

[Identity and access management (IAM)](<https://yellowcube.eu/glossary/identity-and-access-management/>) · [Identity provider (IdP)](<https://yellowcube.eu/glossary/identity-provider/>) · [Federated identity](<https://yellowcube.eu/glossary/federated-identity/>) · [Multi-factor authentication (MFA)](<https://yellowcube.eu/glossary/multi-factor-authentication/>) · [Conditional access](<https://yellowcube.eu/glossary/conditional-access/>)

### Sources

[NIST glossary: Single Sign-On](https://csrc.nist.gov/glossary/term/single_sign_on) · [NIST SP 800-63C-4: Federation and Assertions](https://csrc.nist.gov/pubs/sp/800/63/c/4/final)

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