SAML IDP-initiated SSO fails with cookie_not_found behind NGINX (Keycloak 26)
Add proxy_cookie_flags ~.* secure samesite=None; to the NGINX config (as an ingress annotation if you use ingress-nginx), which marks the Keycloak cookies Secure and SameSite=None so they survive the cross-site IDP POST. Multiple reporters on Keycloak 26.0.x confirmed this fixed the cookie_not_found error. Alternative…
Problem outcome: unknown