The Express request object, which contains original headers like 'x-user-token' if passed by Gateway.
The unique identifier of the media.
The requested action (e.g., 'file', 'thumbnail').
A promise resolving to the media resolution object.
OptionalsecretThe shared secret used to authenticate requests from the API Gateway. If not provided, it will log a warning and accept any request (not recommended for production).
Callback to resolve the media location.