Passing SSO/JWT Token from Fusion SaaS to APEX for REST Data Source Authentication

Environment:

• Oracle APEX (self-hosted, ORDS)
• Oracle Fusion Cloud Applications (SaaS)
• APEX Authentication Scheme: Social Sign-In (OpenID Connect)
• REST Data Sources: Oracle Cloud Applications (SaaS) REST Service type, used to populate page item LOVs

What we're trying to achieve:

We have a custom tile added to the Fusion SaaS Springboard ("Others" section) that launches an APEX application. The tile is configured with an EL expression that appends a JWT (via #{applCoreSecuredToken.trustToken}) to the target APEX URL, so the same authenticated Fusion session/identity can be reused to call Fusion's own SaaS REST APIs directly from APEX — specifically to populate several page item LOVs (e.g., Ledger, Legal Entity, Journal Source) that are backed by REST Data Sources pointing back to Fusion endpoints.