An IdP, or Identity Provider, is the system that verifies a user’s identity and then issues the credentials or tokens that let that user access applications and services. In modern environments, an IdP often sits behind single sign-on, so one successful authentication can unlock many SaaS apps, internal portals, and cloud resources.
IdPs matter because they are a high-value control point. If attackers steal passwords, bypass MFA, or hijack a session, they can abuse the IdP to gain broad access without touching each target application directly. Defenders watch IdP sign-in logs, federation settings, conditional access rules, and token issuance for suspicious behavior. In attacks, the IdP is often the place where credential abuse, phishing, and account takeover become visible; in defense, it is where risky logins can be challenged, blocked, or revoked before access is granted.