Authorisation (not authentication) on SAP-Systems (R/3 & WAS)

Dear ladies and gentlemen,

is there a possibility to separate authentication from authorisation in communications from SAP XI to SAP-Systems (R/3 or WAS)?

Concrete: can we authenticate via RFC-Adapter with userid / pw from communication channel (directory) and authorise use of business functionality (like booking invoices) on SAP-Business-System with another userid sended with the business data?

Thanks,

Daniel