First. Can you confirm with which product of the WebCenter Suite are you working on? As my feeling is that you are posting in the wrong forum
- Oracle WebCenter Portal?
- Oracel WebCenter Content?
- Oracle WebCenter Sites?
As you are talking of OCR I guess you are talking about Oracle WebCenter Enterprise Capture.
I never worked with Oracle Cloud S2S, but I guess it offers a REST API https://docs.oracle.com/en/cloud/saas/procurement/19d/fapra/index.html you can call from On-Premise or On-Cloud version of Oracle WebCenter.