16. RefWorks requires a unique identifier for each user, to associate the user with their RefWorks account. This unique identifier can be either an eduPersonTargetedID (ePTID) or an eduPersonPrincipalName (ePPN). Each IdP may choose to release either the ePTID or the ePPN for their users. Most IdPs choose to release the ePTID, but some prefer to release the ePPN instead. Please note, though, that ePPN may be considered "personal information".