For app=mbw, the gateway forwards the SAMLResponse directly to MBW ACS.
SAMLResponse (required): base64-encoded, signed SAML 2.0 response containing attributes (e.g., memberId, email, groupId, state).app (required): must be mbw → /gateway/acs?app=mbw.SAMLResponse at /gateway/acs?app=mbw.SAMLResponse to MBW ACS:
https://dev-mbw-api.newbenefits.com/Saml2/Acs (configurable in appsettings.json).