JobSink: Reject unauthorized requests

[creydr]

We need to verify in the job-sink, that an request is authorized. Therefor we should do the following in the job sink handler:

• Get the OIDC identity of the sender
• In case the JobSinks .status.policies is set:
  • check, if the senders identity is subject of any of the linked EventPolicies (in their .status.from[]).
    • If it is present: continue with the request
    • If not: reject the request with a 403 status code
• In case the JobSinks .status.policies is empty:
  • Check the default-authorization-mode and do the following depending on its value:
    • allow-all: Continue with the request
    • deny-all: reject the request with a 403 status code
    • allow-same-namespace: check, if the senders identity is from the same namespace, as the Broker. If so, continue with the request, otherwise reject with a 403

For this we can reuse the existing VerifyRequest method from the TokenVerifier and switch from VerifyJWTFromRequest to VerifyRequest (similar as done in #8105).

We should also add an e2e test for the above scenarios

Prerequisites:

• Add Library to support on AuthZ #7985
• Add default-authorization-mode feature flag #7974
• List applying policies in JobSink .status.policies #8062
• Add AuthZ conformance e2e test suite #8149

Additional context:

• Feature track document
• Update TokenVerifier to verify AuthZ too #8063 should help by providing the "verify methods"
• in mt-broker ingress: Reject unauthorized requests #8105 we did the same for the mt-broker-ingress

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