User name in gateway and ECC is mandatory

Hi Experts,

         One of the client is having the requirement like the user dont have access in the backend but he/she can approve by using the SAP Fiori.

For example : The userid for gateway is 'A' , but the user 'A' is not existing in backend.Is it possible to approve the PO using the SAP Fiori.

Thanks in advance.

Regards,

Myilraja