An OmniStudio Developer needs to call an Apex method that handles complex custom authentication and...

A Remote Action is the Integration Procedure element designed to call custom Apex logic. This scenario requires execution of an Apex method that performs custom authentication and token generation before later data retrieval, which is exactly the type of server-side custom logic handled by a Remote Action. A Data Mapper Transform restructures data; it does not execute Apex. A Sub-Integration Procedure calls another Integration Procedure, not an Apex method directly. An HTTP Action calls an external REST endpoint, which is useful after token generation but does not execute local Apex code. Salesforce documentation explicitly states that the Remote Action element calls the specified Apex class and method or an invocable action.

================