Identity Provider (IdP) platforms provide the authentication and single sign-on layer across an organization's application estate — replacing per-application credentials with federated authentication backed by a central directory. Core capabilities include user and group directory (native or synced from HRIS/Active Directory), federation protocol support (SAML 2.0, OIDC, WS-Federation, SCIM for provisioning), multi-factor authentication enforcement, adaptive and risk-based authentication policies, passwordless and passkey support, device trust signals, and an app catalog of pre-built SSO connectors to thousands of SaaS applications. IdP/SSO is the foundational authentication layer every other identity category builds on.