[data-plane] Receiver: Reject unauthorized requests

[creydr]

We need to verify in the receiver (ingress), that an request is authorized. Therefor we should do the following in the receiver:

• Get the OIDC identity of the sender
• In case the resources (Broker/KafkaChannel/KafkaSink) .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 resources .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 resource. If so, continue with the request, otherwise reject with a 403

We should also add an e2e test for the above scenarios.

Additional context:

• Feature track document
• [data-plane] Update TokenVerifier to check for the allowed subjects too #4042 should help by providing the "verify methods"

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[creydr]

/help
/triage accepted

[knative-prow]

@creydr:
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In response to this:

/help
/triage accepted

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[Cali0707]

/area data-plane

[creydr]

Putting back in "Draft" status, as this maybe could be included in #4042 already

[creydr]

Done in #4041 / #4061