Prometheus charm expects ca_file to be the file's text content instead of its path

[michaeldmitry]

Bug Description

When a metrics endpoint provider charm is integrated with prometheus charm, it can set a tls_config as part of its scrape job. This config can contain a ca_file key, which, according to the config spec , should contain the path of the CA cert not the actual contents of the CA. (that usecase is for another field ca)

However, here, the prometheus charm is expecting the ca_file to hold the actual cert content.

So, a charm providing a scrape job config would configure ca_file as per the upstream's definition, but would get unexpected results.

Prometheus charm should fetch the ca key instead.

To Reproduce

1. Deploy a charm setting "tls_config":{"ca_file": "path/to/ca/cert"}
2. Integrate with prometheus over prometheus_scrape interface
3. juju ssh into prometheus container
4. cat /etc/prometheus/prometheus.yaml and grab the value of ca_file in that scrape job
5. cat /filename/from/previous/step and you'll find invalid cert contents

Environment

juju 3.6
microk8s 1.28

Relevant log output

N/A

Additional context

No response