IdP vs SP: What is a Service Provider and an Identity Provider?

Single Sign-On (SSO) is an authentication process that allows users to access multiple applications using a single set of login credentials. The core of any SSO implementation consists of two key players: the Service Provider (SP) and the Identity Provider (IdP). A SP is a website or app that provides services to users, while an IdP stores and manages user identities, authenticating them and passing their identity to SPs. Common IdPs include social platforms like Facebook, Google, and Twitter, as well as Microsoft Entra ID, Okta, JumpCloud, LastPass, ForgeRock, PingFederate, Keycloak, and Google Workspace/Cloud Identity. SPs and IdPs work together to enable SSO by passing authentication requests and user details back and forth. This is facilitated through protocols like SAML (Security Assertion Markup Language) and OpenID Connect (OIDC). There are two main SSO flows: SP-initiated SSO, where the SP redirects the user to the IdP for authentication, and IdP-initiated SSO, where the user logs in first to their IdP and then selects the app they want to log in to from a menu. Implementing SSO can be simplified using platforms like WorkOS, which supports both SP-initiated and IdP-initiated SSO for any major IdP with SDKs for popular platforms and Slack-based support.