IEC TR 62351-90-1:2018(E) addresses the handling of access control of users and automated agents to data objects in power systems by means of role-based access control (RBAC) as defined in IEC TS 62351-8. The main focus of this document lies in developing a standardized method for defining and engineering custom roles, their role-to-right mappings and the corresponding infrastructure support needed to utilize these custom roles in power systems. This publication contains attached files in the form of electronic machine readable files, which are intended to be used as a complement.