Federated identity is a method of identity management that allows users to access multiple applications or systems using a single set of credentials across different domains. It simplifies authentication and enhances security by enabling the creation of a trusted relationship between different identity providers, allowing users to "federate" their identity without each platform storing their login information. Federated identity relies on established protocols such as Security Assertion Markup Language (SAML), OAuth, and OpenID Connect, and offers benefits like simplified user experience, improved security, cross-domain access, and cost and administrative savings. However, it also introduces challenges such as integration complexity, security risks, single point of failure, and vendor lock-in. Federated identity differs from Single Sign-On (SSO) in that SSO is generally about accessing multiple services within a single domain or organization after logging in once, while federated identity spans multiple organizations and allows access across different domains. It also differs from social login, which uses OAuth 2.0 and OIDC exclusively, whereas federated identity might use these protocols or SAML. Overall, federated identity provides a seamless, secure, and efficient way for users to access multiple services with a single set of credentials.