A flaw was found in the SAML brokering component of Keycloak, an identity and access management solution. The issue occurs when Keycloak acts as an intermediary between an upstream identity provider and downstream services. Keycloak fails to respect specific security instructions called ProxyRestrictions in the login messages it receives. This allows a user to log into downstream services even when the original identity provider explicitly forbade further sharing of the login session. As a result, users can bypass security boundaries intended to limit where their identity can be used.