Hi Phil,
for SAML 2 on 7.40 please check the docs on SAML 2. IdP initiated SSO is often also called IdP unsolicited SSO or SAML 2 using unsolicited responses. In the end, only the first roundtrip between browser and SP will be skipped. Without really having any info on your scenario, I would also guess it could work.
Have you just tried to enable SAML2 authentication per the documentation and sent your request to the ABAP system.
Regards,
Patrick
