Federated authentication is a trust arrangement in which one organization or service, called an identity provider, verifies a user and provides evidence of that identity to another service. The receiving service, or service provider, relies on that evidence rather than asking the user to authenticate directly. SAML and OpenID Connect are commonly used to support this model and single sign-on.
This approach simplifies access across connected services, but it makes the trust boundary security-critical. In a SAML login, for example, the service must correctly validate the identity provider’s signed assertion, including its intended recipient and validity period, and reject inappropriate reuse. Weak validation can allow an attacker to bypass authentication. Defenders should keep federation components updated, review identity-provider and service-provider settings, and investigate unusual authentication activity.