By default, OpenSearch has a protected system index, `.opendistro_security`, which you create using [securityadmin.sh]({{site.url}}{{site.baseurl}}/security-plugin/configuration/security-admin/). Even if your user account has read permissions for all indices, you can't directly access the data in this system index.
You can add additional system indices in in `opensearch.yml`. In addition to automatically creating `.opendistro_security`, the demo configuration adds several indices for the various OpenSearch plugins that integrate with the security plugin:
To access these indices, you must authenticate with an [admin certificate]({{site.url}}{{site.baseurl}}/security-plugin/configuration/tls#configure-admin-certificates):