Generate URI of token service via Host in request

[reasonerjt]

This commit update the flow to generate URL of token service, which will first try to use the Host in request. This will help the situation when Harbor is configured to serve via a hostname but some client needs to pull artifacts from Harbor via IP due to limitations in the environment.

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• Well Written Title and Summary of the PR
• Label the PR as needed. "release-note/ignore-for-release, release-note/new-feature, release-note/update, release-note/enhancement, release-note/community, release-note/breaking-change, release-note/docs, release-note/infra, release-note/deprecation"
• Accepted the DCO. Commits without the DCO will delay acceptance.
• Made sure tests are passing and test coverage is added if needed.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed in website repository.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 46.44%. Comparing base (c8c11b4) to head (d335e89).
Report is 468 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #21898      +/-   ##
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+ Coverage   45.36%   46.44%   +1.07%     
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  Files         244      253       +9     
  Lines       13333    14236     +903     
  Branches     2719     2925     +206     
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+ Hits         6049     6612     +563     
- Misses       6983     7273     +290     
- Partials      301      351      +50     

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unittests	46.44% <ø> (+1.07%)	⬆️

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[Copilot]

Pull Request Overview

This PR updates the token service URL generation to prioritize the Host header from the HTTP request, enabling Harbor clients to interact with the service using either hostnames or IP addresses.

• Renamed the function from tokenSvcEndpoint to tokenSvcURL to better reflect its purpose
• Introduced a helper function (getURL) to format the token service URL
• Modified the URL generation logic to utilize req.Host when available

[chlins]

lgtm

[arcezd]

While upgrading from v2.13.1 to v2.14.0, we ran into an issue that might be useful to others

Our harbor is hosted on k8s exposed with Istio, and for some reason, we had this on our virtual service:

rewrite:
  authority: harbor-registry.harbor-registry.svc.cluster.local

Which caused Harbor to reply with the internal cluster svc for the service/token request, instead of the external host registry.example.com: Get "https://harbor-registry.harbor-registry.svc.cluster.local/service/token?

Error response from daemon: Get "https://registry.example.com/v2/project/appimage/manifests/sha256:c0aeeb22fc71e9bd0ac2a4ccbd5b147ff10ea123c49dd9aa6c0d15d62c87716d": Get "https://harbor-registry.harbor-registry.svc.cluster.local/service/token?scope=repository%3Aproject%2Fappimage%3Apull&service=harbor-registry": dial tcp: lookup harbor-registry.harbor-registry.svc.cluster.local on 10.10.10.100:53: no such host

I will blame this on a misconfiguration on our end, but just in case someone else faces the same, I hope this helps figure it out quicker.