With System Center 2019 you can now grant permissions to users on a per cloud basis. This eliminates the need to create a new user role for every combination of action/user/cloud. With System Center 2019 you can create Run As accounts to provide the necessary credentials for performing operations in VMM and use the new capabilities available to the Delegated Administrator and Self-Service User roles to give users the ability to perform tasks.
Windows Admin Center provides the ability to authenticate against the Active Directory domain or from Azure Active Directory. However the RBAC are currently not implemented (July 2019).