The authentication happens in SAP, thus, you must use SAP user and password to connect via jco connection string. Typically, you will need to request your SAP team to create a system user in SAP with the authorization to access BAPIs. Then, you would use jco to build the connection string or connection object with SAP server name, system number, client number, SAP system user name and password.
Thank you! Is RFC ID and client number same or something different?
They are different. "Client number" is provided by your SAP team, usually 3 digits like 300, 800. There is no such term called "RFC ID" in the connection string, but I would assume you probably refer to the RFC connection identification, which is usually specified by yourself to uniquely identify the connection string. Here is an example for jco connection: goenning.net/2014/06/13/connecting-the-world-to-sap-with-rfc
Thank you very much!