message SelfSubjectReviewStatus {
  // User attributes of the user making this request.
  // +optional
  optional k8s.io.api.authentication.v1.UserInfo userInfo = 1;
}

// TokenReview attempts to authenticate a token to a known user.
// Note: TokenReview requests may be cached by the webhook token authenticator
// plugin in the kube-apiserver.
message TokenReview {
  // Standard object's metadata.

ISTIO_ZTUNNEL_BASE_URL="${ISTIO_ZTUNNEL_BASE_URL:-https://storage.googleapis.com/istio-build/ztunnel}"

# If we are not using the default, assume its private and we need to authenticate
if [[ "${ISTIO_ZTUNNEL_BASE_URL}" != "https://storage.googleapis.com/istio-build/ztunnel" ]]; then
  AUTH_HEADER="Authorization: Bearer $(gcloud auth print-access-token)"
  export AUTH_HEADER
fi

# Envoy binary variables
ISTIO_ENVOY_BASE_URL="${ISTIO_ENVOY_BASE_URL:-https://storage.googleapis.com/istio-build/proxy}"

# If we are not using the default, assume its private and we need to authenticate
if [[ "${ISTIO_ENVOY_BASE_URL}" != "https://storage.googleapis.com/istio-build/proxy" ]]; then
  AUTH_HEADER="Authorization: Bearer $(gcloud auth print-access-token)"
  export AUTH_HEADER
fi

This means Ztunnel will have multiple distinct certificates at a time, one for each unique identity (service account) running on its node.

When fetching certificates, ztunnel will authenticate to the CA with its own identity, but request the identity of another workload.
Critically, the CA must enforce that the ztunnel has permission to request that identity.
Requests for identities not running on the node are rejected.

  // token must identify themself with an identifier in the list of
  // audiences of the token, and otherwise should reject the token. A
  // token issued for multiple audiences may be used to authenticate
  // against any of the audiences listed but implies a high degree of
  // trust between the target audiences.
  repeated string audiences = 1;

//
// Kubelets use this API to obtain:
//  1. client certificates to authenticate to kube-apiserver (with the "kubernetes.io/kube-apiserver-client-kubelet" signerName).
//  2. serving certificates for TLS endpoints kube-apiserver can connect to securely (with the "kubernetes.io/kubelet-serving" signerName).
//
// This API can be used to request client certificates to authenticate to kube-apiserver
// (with the "kubernetes.io/kube-apiserver-client" signerName),