do you have a SAP portal in front of your SAP system? In this case WSRP might be an option?
In 2007 we found at help.sap.com some information of how to integrate SAP funtionality into third-party portals. Keeping that in mind, our approach is to have the read/write stuff done by the SAP team and just integrate the resulting (webdynpro?) pages into our jboss-portal by iframes.
A third option, at the lowest level, might be SAP Jco? Our entitlement tema has used that to manage users in the SAP UME.