fix(cors): add 'vary: origin' header if not set by backend

[aslafy-z]

What this PR does / why we need it:

CORS with multiple allowed origin need to serve the 'Vary: Origin' header.
This can be done on the backend side, however, users delegates the CORS setup to their ingress.
For security reason, we disable their use of the snippet annotations, so they can't use it to insert the header.
This change conditionally add the 'Vary' header to 'Origin', if the header is not defined by the backend and the configured allowed origins matches one of these conditions:

• set to any (*)
• set to more than one entry
• contains a wildcard

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• CVE Report (Scanner found CVE and adding report)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation only

Which issue/s this PR fixes

relates to #8469 (comment)

How Has This Been Tested?

• Automatic tests only

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have added unit and/or e2e tests to cover my changes.
• All new and existing tests passed.

[netlify]

✅ Deploy Preview for kubernetes-ingress-nginx canceled.

Name	Link
🔨 Latest commit	8be3706
🔍 Latest deploy log	https://app.netlify.com/projects/kubernetes-ingress-nginx/deploys/6837208b55028800083f8ef5

[k8s-ci-robot]

This issue is currently awaiting triage.

If Ingress contributors determines this is a relevant issue, they will accept it by applying the triage/accepted label and provide further guidance.

The triage/accepted label can be added by org members by writing /triage accepted in a comment.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[k8s-ci-robot]

Hi @aslafy-z. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[larivierec]

That might actually be it.

https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS#access-control-allow-origin

I might have missed it when going through the docs.
There are some tests in Go that will need to be modified however

[larivierec]

Should be roughly around this area for cors annotations.

https://github.com/kubernetes/ingress-nginx/blob/main/test/e2e/annotations/cors.go#L430

[aslafy-z]

@larivierec I implemented a test, feel free to give a look :)

[aslafy-z]

@larivierec I added a conditional to only insert this header when needed and added tests to validate it. Please give a new look.

[larivierec]

lgtm
:)

[aslafy-z]

@rikatz can you please have a look?

[zifeo]

@rikatz Is there something missing from that PR or can it go forward?

[larivierec]

I left my review a year ago, hopefully the maintainers might find time to look at the issue

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: aslafy-z, larivierec
Once this PR has been reviewed and has the lgtm label, please assign gacko for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment