proposal: Support secret providers

[hsmatulis]

This PR adds a proposal to support specifying secrets through secret providers.

TL;DR from doc

TL;DR: This document proposes adding a new way for Prometheus to discover and use secrets from various secret providers, similar to how service discovery works. It introduces a new configuration section where users can specify different secret providers and their configurations. It also defines interfaces and methods for secret providers to implement, allowing for flexibility in how secrets are fetched and managed.

[bwplotka]

Great progress thanks!

[rapphil]

LGTM. can you just update the description of the pull request for posteriority.

[rajagopalanand]

LGTM

[bwplotka]

LGTM generally! Just last nit noted by @rajagopalanand and good to go IMO!

Approving from my side, but I will ask around for a second Prometheus maintainer to have another look

[ArthurSens]

Looks pretty solid :) I just had some small questions

[bwplotka]

Amazing feedback and discussion in https://github.com/prometheus/proposals/pull/47/files#r2041335383

Should we update the proposal with the mentioned alternatives considered?

What do you think is the reasonable solution from this discussion? I see the potential for changing proposal slightly to support the following (for consistency with SD):

password: "<inlined secret>"

password:
  kubernetes:
    namespace: "<ns>"
    name: "<secret name>"
    key: "<data's key for secret name>"

password:
  file:
    path: "<path to secret file>"

[rajagopalanand]

I vote for changing the proposal to be consistent with SD

[saswatamcode]

Thanks! Excited to see this in action. :)

[hsmatulis]

I changed the config style to be more consistent with SD in the proposal. Thanks everyone for all the feedback, and feel free to reach out on the prometheus slack if you have any feedback or ideas. I am working on an implementation for the proposal:)

[bwplotka]

Thanks! @dgl @machine424 -- are you ok to merge? 🤗

[machine424]

lgtm, thanks!

[ArthurSens]

LGTM, one last question :)

[ArthurSens]

Thanks for workin on the proposal, I'm merging as soon as you tell me you're satisfied :)

[hsmatulis]

I think I am ready to merge it, thanks everyone!