Map Kubernetes secret labels to prometheus metrics labels

[deviarchscs]

First of all, thank you for this project!

I have a use case where I need to attach additional info on metrics exposed by ssl-exporter. So far I'm doing a workaround by doing leveraging the relabeling feature of prometheus on the name of the secret, this works but is kind of ugly and I think it would be a real added value of having a way to directly generate prometheus metrics label based on secret labels. See the example below:

Example of secret read by ssl-exporter:

apiVersion: v1
kind: Secret
metadata:
  name: my-secret-tls
  labels:
    ssl-exporter.env: DEV
    ssl-exporter.app: myapp
    ssl-exporter.otherlabel: myotherlabelvalue
type: kubernetes.io/tls
stringData:
  tls.crt: |
    -----BEGIN CERTIFICATE-----
    (...)
    -----END CERTIFICATE-----
  tls.key: ""

I excpect above k8s secret to generate following prometheus metric:

ssl_kubernetes_cert_not_after{env="DEV", app="myapp", otherlabel="myotherlabelvalue", job="...", cn="...", (...)}

Notice how secret labels are transformed into prometheus metrics labels.

I guess the implementation would be done somewhere here:

ssl_exporter/prober/metrics.go

Line 285 in 6037c98

func collectKubernetesSecretMetrics(secrets []v1.Secret, registry *prometheus.Registry) error {

What do you think?