Tier 2: Authenticate clients with provider-specific TLS validation¶

When to use this approach¶

Use Tier 2 X.509 authentication when you need defense-in-depth security but don't have Gateway API v1.5+ yet:

Defense-in-depth security: Same two-layer validation as Tier 1 (TLS + Application)
Older Gateway API versions: Works with Gateway API versions prior to v1.5
Provider flexibility: Supports Istio (via EnvoyFilter) and Envoy Gateway (via EnvoyPatchPolicy)
Migration path: Clear upgrade path to Tier 1 when you adopt Gateway API v1.5+

This approach provides the same security guarantees as Tier 1 but requires provider-specific configuration knowledge.

How it works¶

Tier 2 implements the same two-layer validation model as Tier 1, but uses provider-specific resources for TLS configuration:

Layer 1 (TLS/L4): Gateway validates client certificates during TLS handshake

Configured via EnvoyFilter (Istio) or EnvoyPatchPolicy (Envoy Gateway)
Client presents certificate during mTLS handshake
Gateway validates against configured CA certificates
Invalid, expired, or untrusted certificates are rejected
Gateway sets x-forwarded-client-cert (XFCC) header with certificate details
Incoming XFCC headers from clients are sanitized

Layer 2 (Application/L7): Authorino validates certificates from XFCC header

Identical to Tier 1: AuthPolicy extracts certificate from XFCC header
Applies fine-grained validation using label selectors on CA Secrets
Enables multi-CA trust scenarios

Result: Request proceeds only if both layers succeed.

Before you begin¶

Ensure you have:

Kubernetes cluster: Any supported version
Gateway API: Any version (does not require v1.5)
Gateway implementation: Istio (any version) or Envoy Gateway
Kuadrant Operator: Installed with Kuadrant instance deployed
Provider knowledge: Familiarity with EnvoyFilter (Istio) or EnvoyPatchPolicy (Envoy Gateway)

Choose your provider¶

Select the guide for your gateway provider:

Istio: Configure using EnvoyFilter
Envoy Gateway: Configure using EnvoyPatchPolicy

Both approaches achieve the same security outcome and use identical AuthPolicy configuration.

Istio: EnvoyFilter configuration¶

Step 1: Prepare CA and client certificates¶

Generate or obtain CA and client certificates. Client certificates must include extendedKeyUsage=clientAuth.

# Generate CA
openssl req -x509 -sha512 -nodes \
  -days 365 \
  -newkey rsa:4096 \
  -subj "/CN=Test CA/O=Kuadrant/C=US" \
  -addext basicConstraints=CA:TRUE \
  -addext keyUsage=digitalSignature,keyCertSign \
  -keyout /tmp/ca.key \
  -out /tmp/ca.crt

# Create X.509 v3 extensions for client certificate
cat > /tmp/x509v3.ext << EOF
authorityKeyIdentifier=keyid,issuer
basicConstraints=CA:FALSE
keyUsage=digitalSignature,nonRepudiation,keyEncipherment,dataEncipherment
extendedKeyUsage=clientAuth
EOF

# Generate client certificate
openssl genrsa -out /tmp/client.key 4096
openssl req -new \
  -subj "/CN=test-client/O=Kuadrant/C=US" \
  -key /tmp/client.key \
  -out /tmp/client.csr
openssl x509 -req -sha512 \
  -days 365 \
  -CA /tmp/ca.crt \
  -CAkey /tmp/ca.key \
  -CAcreateserial \
  -extfile /tmp/x509v3.ext \
  -in /tmp/client.csr \
  -out /tmp/client.crt

Important

Client certificates must include extendedKeyUsage=clientAuth for Authorino validation to succeed.

Step 2: Create CA certificate resources¶

# ConfigMap for Gateway TLS validation (Layer 1)
kubectl create configmap client-ca-bundle \
  -n gateway-system \
  --from-file=ca.crt=/tmp/ca.crt

# Secret for Authorino validation (Layer 2)
kubectl create secret generic trusted-client-ca \
  -n kuadrant-system \
  --from-file=ca.crt=/tmp/ca.crt

# Label the secret so Authorino can discover it
kubectl label secret trusted-client-ca \
  -n kuadrant-system \
  authorino.kuadrant.io/managed-by=authorino \
  app.kubernetes.io/name=trusted-client

Step 3: Configure Gateway¶

Create a Gateway without frontend TLS validation (handled by EnvoyFilter instead):

kubectl apply -f https://raw.githubusercontent.com/Kuadrant/kuadrant-operator/refs/heads/main/examples/x509-authentication/gateway-tier2-istio.yaml

This creates:

cert-manager Issuer: Self-signed certificate issuer for the gateway server certificate
TLSPolicy: Kuadrant policy to manage the gateway's server TLS certificate
ConfigMap: Infrastructure configuration to mount the CA certificate bundle into gateway pods
Gateway: Standard Gateway with infrastructure.parametersRef pointing to the ConfigMap (client certificate validation handled by EnvoyFilter)

Step 4: Create EnvoyFilter for mTLS validation¶

Create an EnvoyFilter to configure Envoy's DownstreamTlsContext for client certificate validation:

kubectl apply -f -<<EOF
apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: mtls-validation
  namespace: gateway-system
spec:
  targetRefs:

  - group: gateway.networking.k8s.io
    kind: Gateway
    name: mtls-gateway
  configPatches:
  - applyTo: FILTER_CHAIN
    match:
      context: GATEWAY
      listener:
        portNumber: 443
    patch:
      operation: MERGE
      value:
        transport_socket:
          name: envoy.transport_sockets.tls
          typed_config:
            "@type": type.googleapis.com/envoy.extensions.transport_sockets.tls.v3.DownstreamTlsContext
            commonTlsContext:
              validationContext:
                trustedCa:
                  filename: /etc/certs/ca.crt
            requireClientCertificate: true
EOF

Step 5: Deploy application and create HTTPRoute¶

# Deploy httpbin application
kubectl apply -f https://raw.githubusercontent.com/Kuadrant/kuadrant-operator/refs/heads/main/examples/x509-authentication/httpbin.yaml

# Create HTTPRoute
kubectl apply -f https://raw.githubusercontent.com/Kuadrant/kuadrant-operator/refs/heads/main/examples/x509-authentication/httproute.yaml

Step 6: Configure AuthPolicy¶

The AuthPolicy configuration is identical to Tier 1 - it extracts the certificate from the XFCC header and validates it:

kubectl apply -f https://raw.githubusercontent.com/Kuadrant/kuadrant-operator/refs/heads/main/examples/x509-authentication/authpolicy.yaml

This creates an AuthPolicy that:

Extracts the certificate from the x-forwarded-client-cert header
Validates the certificate chain against CA certificates labeled app.kubernetes.io/name: trusted-client
Enforces authorization based on certificate Organization attribute
Injects certificate attributes into request headers

Envoy Gateway: EnvoyPatchPolicy configuration¶

Step 1: Prepare CA and client certificates¶

Same as Istio (see Istio Step 1)

Step 2: Create CA certificate resources¶

Same as Istio (see Istio Step 2)

Step 3: Configure Gateway¶

Create a Gateway without frontend TLS validation (handled by EnvoyPatchPolicy instead):

kubectl apply -f https://raw.githubusercontent.com/Kuadrant/kuadrant-operator/refs/heads/main/examples/x509-authentication/gateway-tier2-envoygateway.yaml

This creates:

cert-manager Issuer: Self-signed certificate issuer for the gateway server certificate
TLSPolicy: Kuadrant policy to manage the gateway's server TLS certificate
EnvoyProxy: Custom resource to mount the CA certificate bundle into gateway pods
Gateway: Standard Gateway with infrastructure.parametersRef pointing to the EnvoyProxy resource (client certificate validation handled by EnvoyPatchPolicy)

Note

Unlike Istio which uses a plain ConfigMap, Envoy Gateway requires an EnvoyProxy custom resource for infrastructure configuration. The EnvoyProxy resource defines pod volumes and container volume mounts.

Step 4: Create EnvoyPatchPolicy for mTLS validation¶

Create an EnvoyPatchPolicy to configure client certificate validation:

kubectl apply -f -<<EOF
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: EnvoyPatchPolicy
metadata:
  name: mtls-validation
  namespace: gateway-system
spec:
  targetRef:
    group: gateway.networking.k8s.io
    kind: Gateway
    name: mtls-gateway
  type: JSONPatch
  jsonPatches:

  - type: "type.googleapis.com/envoy.config.listener.v3.Listener"
    name: https
    operation:
      op: add
      path: "/filter_chains/0/transport_socket/typed_config/commonTlsContext/validationContext"
      value:
        trustedCa:
          filename: /etc/certs/ca.crt
  - type: "type.googleapis.com/envoy.config.listener.v3.Listener"
    name: https
    operation:
      op: add
      path: "/filter_chains/0/transport_socket/typed_config/requireClientCertificate"
      value: true
EOF

Step 5: Deploy application and create HTTPRoute¶

Same as Istio (see Istio Step 5)

Step 6: Configure AuthPolicy¶

Same as Istio (see Istio Step 6)

Verify defense-in-depth security¶

Testing is identical to Tier 1. Run the same test scenarios:

GATEWAY_IP=$(kubectl get gateway mtls-gateway -n gateway-system -o jsonpath='{.status.addresses[0].value}')

# Test 1: Valid certificate → HTTP 200
curl -ik https://httpbin.$GATEWAY_IP.nip.io/get \
  --cert /tmp/client.crt \
  --key /tmp/client.key

# Test 2: No certificate → TLS handshake fails
curl -ik https://httpbin.$GATEWAY_IP.nip.io/get

# Test 3: Untrusted certificate → TLS handshake fails
curl -ik https://httpbin.$GATEWAY_IP.nip.io/get \
  --cert /tmp/untrusted.crt \
  --key /tmp/untrusted.key

# Test 4: Valid cert, wrong attributes → HTTP 403
curl -ik https://httpbin.$GATEWAY_IP.nip.io/get \
  --cert /tmp/unauthorized-client.crt \
  --key /tmp/unauthorized-client.key

Migration to Tier 1¶

When you upgrade to Gateway API v1.5+ and your gateway provider supports spec.tls.frontend.default.validation, migrate from Tier 2 to Tier 1:

Migration steps¶

Update Gateway resource to include frontend TLS validation:

spec:
  tls:
    frontend:
      default:
        validation:
          caCertificateRefs:
          - name: client-ca-bundle
            kind: ConfigMap
          mode: AllowValidOnly

Remove provider-specific resource:

# For Istio
kubectl delete envoyfilter mtls-validation -n gateway-system

# For Envoy Gateway
kubectl delete envoypatchpolicy mtls-validation -n gateway-system

Keep AuthPolicy unchanged: AuthPolicy configuration remains identical
Verify: Run the same test scenarios to confirm migration succeeded

Why migrate?¶

Standardization: Uses Gateway API standard instead of vendor-specific resources
Maintainability: Simpler configuration, easier to understand
Portability: Gateway API configuration is portable across providers
Future-proof: Gateway API v1.5 is the recommended approach going forward

Troubleshooting¶

EnvoyFilter not applied¶

Symptoms: TLS handshake succeeds without client certificate

Resolution:

# Verify EnvoyFilter exists
kubectl get envoyfilter mtls-validation -n gateway-system

# Check targetRef points to gateway
kubectl get envoyfilter mtls-validation -n gateway-system -o yaml | grep -A 3 targetRefs

# Check Envoy configuration was patched
kubectl exec -n gateway-system \
  $(kubectl get pod -n gateway-system -l gateway.networking.k8s.io/gateway-name=mtls-gateway -o jsonpath='{.items[0].metadata.name}') \
  -- curl -s localhost:15000/config_dump?include_eds | grep -A 20 validation_context

CA certificate not mounted¶

Symptoms: Gateway logs show "failed to load trusted CA"

Resolution:

# Verify ConfigMap exists
kubectl get configmap client-ca-bundle -n gateway-system

# Check volume mount in gateway pod
kubectl describe pod -n gateway-system -l gateway.networking.k8s.io/gateway-name=mtls-gateway | grep -A 5 Mounts

# Verify file exists in pod
kubectl exec -n gateway-system \
  $(kubectl get pod -n gateway-system -l gateway.networking.k8s.io/gateway-name=mtls-gateway -o jsonpath='{.items[0].metadata.name}') \
  -- cat /etc/certs/ca.crt

XFCC header not set correctly¶

Symptoms: Authorino rejects with "certificate not found"

Resolution:

# Verify forward_client_cert_details configuration
kubectl exec -n gateway-system \
  $(kubectl get pod -n gateway-system -l gateway.networking.k8s.io/gateway-name=mtls-gateway -o jsonpath='{.items[0].metadata.name}') \
  -- curl -s localhost:15000/config_dump?include_eds | grep -i forward_client_cert

# Check Envoy access logs for XFCC
kubectl logs -n gateway-system -l gateway.networking.k8s.io/gateway-name=mtls-gateway | grep XFCC

Tier 2: Authenticate clients with provider-specific TLS validation¶

When to use this approach¶

How it works¶

Before you begin¶

Choose your provider¶

Istio: EnvoyFilter configuration¶

Step 1: Prepare CA and client certificates¶

Step 2: Create CA certificate resources¶

Step 3: Configure Gateway¶

Step 4: Create EnvoyFilter for mTLS validation¶

Step 5: Deploy application and create HTTPRoute¶

Step 6: Configure AuthPolicy¶

Envoy Gateway: EnvoyPatchPolicy configuration¶

Step 1: Prepare CA and client certificates¶

Step 2: Create CA certificate resources¶

Step 3: Configure Gateway¶

Step 4: Create EnvoyPatchPolicy for mTLS validation¶

Step 5: Deploy application and create HTTPRoute¶

Step 6: Configure AuthPolicy¶

Verify defense-in-depth security¶

Migration to Tier 1¶

Migration steps¶

Why migrate?¶

Troubleshooting¶

EnvoyFilter not applied¶

CA certificate not mounted¶

XFCC header not set correctly¶

See also¶