For trusted system access to an SAP Fiori back-end server, the authorization object S_RFCACL is required. S_RFCACL (RFC Authorization for Trusted Systems) controls access in trusted RFC (Remote Function Call) connections, which are used to establish secure communication between the Fiori front-end server and the back-end server. This object ensures that only authorized systems or users can execute RFC calls in a trusted relationship, verifying the calling system’s identity and the user’s permissions. It is critical for securing Fiori app access, as these apps rely on RFC connections to retrieve data from the back-end. S_START is used for starting Fiori apps, S_SERVICE governs OData service access, and S_RFC controls general RFC access but lacks the trusted system specificity of S_RFCACL. By requiring S_RFCACL, SAP ensures that trusted connections are tightly controlled, preventing unauthorized access and maintaining the integrity of Fiori back-end interactions in SAP S/4HANA systems.