conformance: normative test for backend client certificate in Gateway

[snorwin]

What type of PR is this?

/kind test
/area conformance-test

What this PR does / why we need it:
Adds a normative conformance test for .spec.tls.backend.clientCertificateRef. The test verifies that the configured client certificate is presented when connecting to a backend over TLS.

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[snorwin]

/cc @rikatz @kl52752

No rush on this, just whenever you have a moment. I was working on the feature in our implementation and thought it might be a good idea to propose a conformance test early.

[rikatz]

/assign
Will take a look next week :D happy weekend!

[snorwin]

/test all

[kl52752]

thanks for PR, LGTM!

[snorwin]

/assign @robscott

[youngnick]

This LGTM from what I can see, thanks @snorwin.

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kl52752, snorwin, youngnick

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[snorwin]

@arkodg is presenting a client certificate to the upstream based on .spec.tls.backend already implemented in Envoy Gateway? If so, I’d appreciate it if someone could review and verify this new conformance test.

I’ve already validated it using the Airlock Microgateway.

[arkodg]

hey @snorwin this is not yet implemented in Envoy Gateway ( tracked with envoyproxy/gateway#4381)