SAML
Security Assertion Markup Language. XML assertions from an identity provider so a service can skip local passwords.
SAML is a federated login protocol. An identity provider authenticates the user and sends a signed assertion to a service provider. The service trusts the identity provider's keys, not a password stored in the app. Common in enterprise single sign-on.
Keep current libraries and rotate signing certificates before they expire. Stale metadata breaks logins in cheap ways. SAML is not authorisation by itself. The assertion can carry groups; the application still has to enforce them.
See also: OpenID Connect, Identity and access management, Authentication, Multi-factor authentication.