src/main/features/base.json

{
    "bundles": [
        {
            "id": "org.apache.sling:org.apache.sling.thumbnails:${project.version}",
            "start-order": "20"
        }
    ],
    "configurations":{
        "org.apache.sling.serviceusermapping.impl.ServiceUserMapperImpl.amended~sling-thumbnails":{
            "user.mapping":[
                "org.apache.sling.thumbnails:sling-thumbnails=[sling-thumbnails]"
            ]
        }
    },
    "repoinit:TEXT|true": [
        "create service user sling-thumbnails with path system/sling",
        "set principal ACL for sling-thumbnails",
        "allow   jcr:write,jcr:nodeTypeManagement,jcr:versionManagement    on /content",
        "allow   jcr:read    on /",
        "end"
        
    ]
}