[RFC-0010] Validate artifact repository for all auth providers

[matheuscscp]

Part of: fluxcd/flux2#5022

Copying a few missing things from the old code at oci/auth. Also renamed a few things and improved tests.

After this change oci/auth becomes completely obsolete, so I'm also removing it and moving oci/client into oci.

[stefanprodan]

We need to run the OCI e2e tests for AWS and GCP, to unblock them please fix: Error: ./azure_test.go:156:23: non-constant format string in call to fmt.Errorf. You can trigger both tests manually:

• https://github.com/fluxcd/pkg/actions/workflows/integration-gcp.yaml
• https://github.com/fluxcd/pkg/actions/workflows/integration-aws.yaml

[matheuscscp]

Looks like GCP is still blocked by another issue:

2025/05/04 21:39:17 panic: Failed to create and push images:
GET https://gcr.io/v2/token?scope=repository%3Acncf-flux%2Ft6r2d%3Apush%2Cpull&service=gcr.io:
unexpected status code 412 Precondition Failed: Container Registry is deprecated and shutting down,
please use the auto migration tool to migrate to Artifact Registry (gcloud artifacts docker upgrade migrate
--projects='cncf-flux').
For more details see: https://cloud.google.com/artifact-registry/docs/transition/auto-migrate-gcr-ar

AWS seems legit:

https://github.com/fluxcd/pkg/actions/runs/14825330641/job/41617697072

How can I get access to the AWS infra to troubleshoot?

[matheuscscp]

I really need to look into why the AWS integration tests are failing, since fixing the linter problem fixes the tests. I created a branch only for checking this: https://github.com/fluxcd/pkg/actions/runs/14843735405/job/41672551135

However, I manually tested these changes across all the Flux APIs for container registries, all three cloud providers, both at controller and object-level:

fluxcd/image-reflector-controller#760

fluxcd/source-controller#1790

Everything is working.

[matheuscscp]

Both AWS and GCP integration tests are now passing!

https://github.com/fluxcd/pkg/actions/runs/14887443881/job/41810713895

https://github.com/fluxcd/pkg/actions/runs/14887396557/job/41810550558

[stefanprodan]

LGTM

Thanks @matheuscscp 🥇