SQL Server Reporting Services (Groups)
In the Specify Read-Only Group, specify the group to whom you want to grant read-only access to Monitoring reports. Use the format <domain>\<access group>. For example: contoso\RTCUniversalReadOnlyAdmins.
Assigning a group read-only access is optional. If you do not want to grant read-only access now, you can configure it later directly in SQL Server Reporting Services.