In the absence of a suitable Oracle web service, we've implemented a downloading solution using a BI Report. The data downloaded through the BI Report leverages some, but not all, of the access controls used in the Oracle Fusion ERP UI.
To ensure only authorized users can access information, administrators manage download access through a profile option. Failure to correctly set this profile option for the Customer Integrator will result in no records being able to be downloaded: note that there will be no error message in this situation.