What is a SAML Assertion in Single Sign-On?

A practitioner-focused explainer of SAML assertions in enterprise SSO, describing their role as signed XML “trust tokens” between IdPs and SPs, the three assertion types (authentication, attribute, authorization), key XML elements (Issuer, Signature, Subject, Conditions), and the difference between a SAML Response and an Assertion. It outlines security safeguards (XML signatures, TLS, tight validity windows, audience restrictions), common vulnerabilities and attacks (XML Signature Wrapping, replay, MitM) with mitigations, a validation checklist (signature, time, audience, issuer, replay), troubleshooting tips, and guidance on when to use SAML versus OIDC.