The metrics vhost forwarded the store's read API (query, series, labels,
export, vmui, ...) with no credential, so anything that could reach
metrics.<swarm> could read every hive's and agent's metrics. mara ruled on
checked by an auth_request responder, and operators use their authelia
session.
- swarm-metrics-auth (new crate): auth_request responder on the metrics
store's host. Compares the presented bearer, in constant time, with the
one stored at swarm/services/<grafana client id>/metrics/bearer, read
under its own bao leaf and cached for 60s. Static user, the post-#5264
swarm-logs-auth unit shape.
- swarm-bao-grafana-metrics-bearer: on Grafana's host, creates that bearer
in bao if absent (create without update, Grafana's existing leaf) and
writes "Bearer <value>" into the container; the datasource sends it as
its Authorization header via $__file{}.
- The vhost: read locations take auth_request through a map (a bearer goes
to swarm-metrics-auth, anything else to authelia, no login redirect);
vmui takes an authelia session with the login redirect; forceSSL like
the logs vhost. The authelia subrequest location is renamed from
/__metrics_push_authz to /__metrics_authelia since it now serves reads.
- Authelia: the collector keeps every path; everyone else is refused the
collector's push and /metrics paths; group admins is admitted to the
rest; then deny.
- bao: a swarm-metrics-auth cert role and policy (read on the one leaf),
its leaf minted by glue-bao-tls, the CN reserved as a hive name, and
Grafana's grant gains create on the bearer leaf.
Fixes#3596
