Ok this gets complicated. cephadm doesn't support SSL at this point. See https://bugzilla.redhat.com/show_bug.cgi?id=1994251 cephadm doesn't support deploying additional files for existing daemon types. See https://prometheus.io/docs/guides/basic-auth/#creating-web-yml and --- For now you can manually deploy your own Prometheus and Grafana. Does this help?
relates to https://bugzilla.redhat.com/show_bug.cgi?id=2028173
Support for the first part (basic auth) has been add by the following upstream PR: https://github.com/ceph/ceph/pull/46601. More changes are needed to make the authentication configurable.