BS PD IEC TR 62351-90-1:2018, which is a technical report, addresses the handling of access controlof users and automated agents to data objects in power systems by means of role-basedaccess control (RBAC) as defined in IEC TS 62351-8. IEC TS 62351-8 defines three differentprofiles to distribute role information and also defines a set of mandatory roles to besupported. Adoption of RBAC has shown that the defined mandatory roles are not alwayssufficient and it is recommended that the method for defining custom roles be standardized toensure interoperability. Hence, the main focus of this document lies in developing astandardized method for defining and engineering custom roles, their role-to-right mappingsand the corresponding infrastructure support needed to utilize these custom roles in powersystems. This is achieved by defining categories and sub level categories, which provide adistinction of actions, connected with dedicated rights as well as a proposal for a format todistribute the custom role-to-right mappings. Moreover, a format is being proposed todistribute the information on custom defined roles and associated rights by utilizing XACML asan established standard for access control.