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Integrating IAP with Cloud Service Mesh

This guide describes how to integrate Identity-Aware Proxy (IAP) with Cloud Service Mesh. The IAP integration with Cloud Service Mesh enables you to safely access services based on Google's BeyondCorp principles. IAP verifies user identity and context of the request to determine if a user should be allowed to access an application or resource. The IAP integration with Cloud Service Mesh provides you with the following benefits:

Complete context-aware access control to the workloads running on Cloud Service Mesh. You can set fine-grained access policies based on attributes of the originating request, such as user identity, the IP address, and device type. You can combine your access policies with restrictions based on the hostname and path of a request URL.
Enable support for context-aware claims in Cloud Service Mesh authorization.
Scalable, secure, and highly available access to your application through a Google Cloud load balancer. High performance load balancing provides built-in protection of distributed denial-of-service (DDoS) attacks and support for global anycast IP addressing.

Prerequisites

Follow the steps in Install dependent tools and validate cluster to:

Additionally, this guide assumes that you have:

Setting up a cluster with Cloud Service Mesh

This section explains how to get set up for the IAP integration for both new installations of Cloud Service Mesh and upgrades.

New installations

Enable iap.googleapis.com. In the following command, replace PROJECT_IDwith the project that you will install Cloud Service Mesh in:
```
gcloud services enable \
  --project=PROJECT_ID \
  iap.googleapis.com
```
The cluster that you are updating must have the --addons=HttpLoadBalancing option set. The HttpLoadBalancing add-on enables an HTTP (L7) load balancing controller for the cluster. Run the following command to update the cluster with the options required by Cloud Service Mesh. Unless you've set a default zone or region, you need to supply the region (--region=REGION) or zone (--zone=ZONE) in the command.
```
gcloud container clusters update CLUSTER_NAME \
  --project=PROJECT_ID \
  --update-addons=HttpLoadBalancing=ENABLED
```
By default, the iap-operator.yaml file has port 31223 set as the status port, and port 31224 set as the http port. If port 31223 is already in use in your cluster, run the following to set another status port:

Important: You must use a kpt version earlier than v1.0.
```
kpt cfg set asm gcloud.container.cluster.ingress.statusPort STATUS_PORT
```
If port 31224 is already in use in your cluster, run the following to set another http port:
```
kpt cfg set asm gcloud.container.cluster.ingress.httpPort HTTP_PORT
```
Follow the steps in Install default features and Mesh CA to use a Google-provided script to install Cloud Service Mesh. When you run the script, include the following option:
```
--option iap-operator
```
For example:
```
./asmcli install \
  --project_id "PROJECT_ID" \
  --cluster_name "CLUSTER_NAME" \
  --cluster_location "CLUSTER_LOCATION" \
  --fleet_id FLEET_PROJECT_ID \
  --output_dir DIR_PATH \
  --enable_all \
  --option iap-operator
```
When you install Cloud Service Mesh, the iap-operator.yaml file sets the type field on the istio-ingressgateway service to NodePort, which configures the gateway to open a specific port on the service mesh. This allows you to set up a load balancer, which routes traffic sent to your domain name to this port.
If you are installing managed Cloud Service Mesh, then also complete the following steps:
1. Add the revision label to the istio-system namespace.
2. Download the Istio ingress gateway service spec for IAP and name it iap_operator.yaml.
3. Install the ingress as a NodePort service. For more information, see Migrate from IstioOperator.
```
asmcli experimental mcp-migrate-check -f iap_operator.yaml

istioctl install -f /asm-generated-configs/gateways-istiooperator/"GATEWAY_NAME".yaml
```

After installing Cloud Service Mesh, return to this guide and continue with the next section to set up the integration with IAP.

Upgrades

This section covers the following upgrade use cases:

You have already set up the IAP integration and you are upgrading Cloud Service Mesh. In this case, you have already enabled iap.googleapis.com on your project and the HttpLoadBalancing add-on on your cluster. Skip to step 3, to download the asm package and upgrade Cloud Service Mesh.
You are upgrading Cloud Service Mesh and you want to set up the integration with IAP for the first time. In this case, you need to complete all of the following steps, upgrade Cloud Service Mesh, and return to this guide after the upgrade to complete the integration.

Enable iap.googleapis.com. In the following command, replace PROJECT_IDwith the project that you will install Cloud Service Mesh in.
```
gcloud services enable \
  --project=PROJECT_ID \
  iap.googleapis.com
```
The cluster that you are updating must have the --addons=HttpLoadBalancing option set. The HttpLoadBalancing add-on enables an HTTP (L7) load balancing controller for the cluster. Run the following command to update the cluster with the options required by Cloud Service Mesh. Unless you've set a default zone or region, you need to supply the region (--region=REGION) or zone (--zone=ZONE) in the command.
```
gcloud container clusters update CLUSTER_NAME \
  --project=PROJECT_ID
  --update-addons=HttpLoadBalancing=ENABLED
```

If you are updating an existing, functioning HTTP Cloud Load Balancer, run the following to preserve your existing http and status ports:

kpt cfg set asm gcloud.container.cluster.ingress.httpPort $(kubectl -n istio-system get service istio-ingressgateway -o jsonpath='{.spec.ports[?(@.name=="http2")].nodePort}')

kpt cfg set asm gcloud.container.cluster.ingress.statusPort $(kubectl -n istio-system get service istio-ingressgateway -o jsonpath='{.spec.ports[?(@.name=="status-port")].nodePort}')

Follow the steps in Upgrading Cloud Service Mesh to use a Google-provided script to upgrade Cloud Service Mesh.

When you upgrade Cloud Service Mesh, the iap-operator.yaml file sets the type field on the istio-ingressgateway service to NodePort, which configures the gateway to open a specific port on the service mesh. This allows you to set up a load balancer, which routes traffic sent to your domain name to this port.

By default, the iap-operator.yaml file has port 31223 set as the status port, and port 31224 set as the http port.

When you run the script, include the following option:
```
--option iap-operator
```
For example:
```
./asmcli install \
  --project_id "PROJECT_ID" \
  --cluster_name "CLUSTER_NAME" \
  --cluster_location "CLUSTER_LOCATION" \
  --fleet_id FLEET_PROJECT_ID \
  --output_dir DIR_PATH \
  --enable_all \
  --option iap-operator
```
Complete the upgrade by triggering automatic sidecar proxy injection on your workloads. For details, see Deploying and redeploying workloads.

After completing the upgrade, return to this guide and continue with the next section to set up the integration with IAP.

Reserving a static IP address and configuring DNS

To integrate Identity-Aware Proxy with Cloud Service Mesh, you have to set up a Google Cloud HTTP(S) load balancer, which requires a domain name that points to a static IP address. You can reserve a static external IP address, which assigns the address to your project indefinitely until you explicitly release it.

Reserve a static external IP address:

gcloud compute addresses create example-static-ip --global

Get the static IP address:

gcloud compute addresses describe example-static-ip --global

In your domain name registrar, configure a fully qualified domain name (FQDN) with the static IP address. Typically, you add an A record to your DNS settings. The configuration steps and terminology for adding an A record for a FQDN vary depending on your domain name registrar.

It can take 24 to 48 hours for the DNS setting to propagate. You can continue setting up everything in this guide, but you won't be able to test the setup until the DNS settings propagate.

Deploying a sample application

Before you enable IAP, you need an application running on your GKE cluster so you can verify that all requests have an identity. This guide uses the Bookinfo sample to demonstrate how to setup the HTTP(S) load balancer and enable IAP.

Follow the steps to deploy Bookinfo. Until you deploy the load balancer, the Bookinfo application isn't accessible outside of your GKE cluster (such as from a browser).

External requests

Bookinfo's Gateway resource (defined in samples/bookinfo/networking/bookinfo-gateway.yaml) uses the preconfigured istio-ingressgateway. Recall that when you deployed Cloud Service Mesh, you specified NodePort for the istio-ingressgateway, which opens a specific port on the service mesh. Although the nodes in your cluster have external IP addresses, requests coming from outside your cluster are blocked by Google Cloud firewall rules. With IAP, the correct way to expose applications to the public internet is by using a load balancer. Don't expose the node addresses using firewall rules, which would bypass IAP.

To route requests to Bookinfo, you set up an HTTP(S) load balancer in your Google Cloud project. Because the load balancer is in your project, it is inside of the firewall and can access the nodes in your cluster. After you configure the load balancer with the static IP address and your domain name, you can send requests to the domain name, and the load balancer forwards the requests to the nodes in the cluster.

Enabling IAP

The following steps describe how to enable IAP.

Configuring consent screen

Check if you already have an existing brand by using the list command. You may only have one brand per project.
```
gcloud iap oauth-brands list
```
The following is an example gcloud response, if the brand exists:
```
name: projects/[PROJECT_NUMBER]/brands/[BRAND_ID]
applicationTitle: [APPLICATION_TITLE]
supportEmail: [SUPPORT_EMAIL]
orgInternalOnly: true
```
Note: If a brand already exists for a project and has been configured for external users (orgInternalOnly: false), but you want to restrict it to internal users, you must make that change manually from the OAuth consent screen in order to create OAuth clients with this API.
If no brand exists, use the create command:
```
gcloud iap oauth-brands create --application_title=APPLICATION_TITLE --support_email=SUPPORT_EMAIL
```
The above fields are required when calling this API:
- supportEmail: The support email displayed on the OAuth consent screen. This email address can either be a user's address or a Google Groups alias. While service accounts also have an email address, they are not actual valid email addresses, and cannot be used when creating a brand. However, a service account can be the owner of a Google Group. Either create a new Google Group or configure an existing group and set the desired service account as an owner of the group.
  
  Note: The user issuing the request must be an owner of the specified support email address.
- applicationTitle: The application name displayed on OAuth consent screen.
The response contains the following fields:
```
name: projects/[PROJECT_NUMBER]/brands/[BRAND_ID]
applicationTitle: [APPLICATION_TITLE]
supportEmail: [SUPPORT_EMAIL]
orgInternalOnly: true
```

Creating an IAP OAuth Client

Use the create command to create a client. Use the brand name from previous step.

gcloud iap oauth-clients create projects/PROJECT_NUMBER/brands/BRAND-ID --display_name=NAME

The response contains the following fields:

name: projects/[PROJECT_NUMBER]/brands/[BRAND_NAME]/identityAwareProxyClients/[CLIENT_ID]
secret: [CLIENT_SECRET]
displayName: [NAME]

Use the client ID (CLIENT_ID in the above step) and CLIENT_SECRET to enable IAP. Create a kubernetes secret with the materials from your OAuth Client:
```
kubectl create secret generic -n istio-system my-secret --from-literal=client_id=CLIENT_ID \
--from-literal=client_secret=CLIENT_SECRET
```

Deploying the load balancer

You can use an Ingress resource to create an HTTP(S) load balancer with automatically configured SSL certificates. Managed SSL certificates are provisioned, renewed, and managed for your domain.

Create a ManagedCertificate resource. This resource specifies the domain for the SSL certificate. The spec.domains list must contain only one domain. Wildcard domains aren't supported. In the following YAML, replace DOMAIN_NAME with the domain name that you configured for the external static IP address.
```
cat <<EOF | kubectl apply -f -
apiVersion: networking.gke.io/v1
kind: ManagedCertificate
metadata:
  name: example-certificate
  namespace: istio-system
spec:
  domains:
    - DOMAIN_NAME
EOF
```

Create a BackendConfig resource. This resource instructs GCLB how to perform Health Checks on the Ingress Gateway, as well as configure Identity-Aware Proxy. First, collect a few values from the Ingress Gateway about health checks:

Health check ingress port: This is the health check port of istio-ingress.

export HC_INGRESS_PORT=$(kubectl -n istio-system get service istio-ingressgateway -o jsonpath='{.spec.ports[?(@.name=="status-port")].nodePort}')

Health check ingress path: This is the health check path of istio-ingress.

export HC_INGRESS_PATH=$(kubectl get pods -n istio-system -l app=istio-ingressgateway -o jsonpath='{.items[0].spec.containers[?(@.name=="istio-proxy")].readinessProbe.httpGet.path}')

cat <<EOF | kubectl apply -n istio-system -f -
apiVersion: cloud.google.com/v1
kind: BackendConfig
metadata:
  name: http-hc-config
spec:
  healthCheck:
    checkIntervalSec: 2
    timeoutSec: 1
    healthyThreshold: 1
    unhealthyThreshold: 10
    port: ${HC_INGRESS_PORT}
    type: HTTP
    requestPath: ${HC_INGRESS_PATH}
  iap:
    enabled: true
    oauthclientCredentials:
      secretName: my-secret
EOF

Annotate the ingress service with your BackendConfig.

    kubectl annotate -n istio-system service/istio-ingressgateway --overwrite \
      cloud.google.com/backend-config='{"default": "http-hc-config"}' \
      cloud.google.com/neg='{"ingress":false}'

Create the load balancer by defining the Ingress resource.
- Set the networking.gke.io/managed-certificates annotation to the name of the certificate you created in the previous step, example-certificate.
- Set the kubernetes.io/ingress.global-static-ip-name annotation to the name of the static IP address you reserved, example-static-ip.
- Set the serviceName to istio-ingressgateway, which is used in the Gateway resource for the Bookinfo sample.
```
cat <<EOF | kubectl apply -f -
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: example-ingress
  namespace: istio-system
  annotations:
    kubernetes.io/ingress.global-static-ip-name: example-static-ip
    networking.gke.io/managed-certificates: example-certificate
spec:
  defaultBackend:
    service:
      name: istio-ingressgateway
      port:
        number: 80
EOF
```
Note: It can take up to 10-20 minutes for the load balancer to be functional.
In the Google Cloud console, go to the Kubernetes Engine > Services & Ingress page.

Go to the Services & Ingress page

You should see the "Creating ingress" message in the Status column. Wait for GKE to fully provision the Ingress before continuing. Refresh the page every few minutes to get the most up-to-date status on the Ingress. After the Ingress is provisioned, you might see the "Ok" status, or the error "All backend services are in UNHEALTHY state." One of the resources that GKE provisions is a default health check. If you see the error message, that indicates that the Ingress is provisioned and that the default health check ran. When you see either the "Ok" status or the error, continue with the next section to configure the health checks for the load balancer.

Configure the IAP access list

Add a user to the access policy for IAP:

gcloud beta iap web add-iam-policy-binding \
    --member=user:EMAIL_ADDRESS \
    --role=roles/iap.httpsResourceAccessor

where EMAIL_ADDRESS is the user's full email address such as alice@example.com.

Test the load balancer. Point your browser to:
```
http://DOMAIN_NAME/productpage
```
where DOMAIN_NAME is the domain name that you configured with the external static IP address.

You should see the Bookinfo application's productpage. If you refresh the page several times, you should see different versions of reviews, presented in a round robin style: red stars, black stars, no stars.

You should also test https access to Bookinfo.

Enable RCToken support on the service mesh

By default, IAP generates a JSON Web Token (JWT) that is scoped to the OAuth client. For Cloud Service Mesh, you can configure IAP to generate a RequestContextToken (RCToken), which is a JWT but with a configurable audience. RCToken lets you configure the audience of the JWT to an arbitrary string, which can be used in the Cloud Service Mesh policies for fine-grained authorization.

To configure the RCToken:

Create an environment variable for the RCToken audience. This can be any string that you want.
```
export RCTOKEN_AUD="your-rctoken-aud"
```
Optional: The following step requires the BACKEND_SERVICE_ID. If you need to find out the BACKEND_SERVICE_ID, run the following command:
```
kubectl -n istio-system get Ingress example-ingress -o json | jq \
 '.metadata.annotations."ingress.kubernetes.io/backends"'
```
The expected output is similar to "{\"BACKEND_SERVICE_ID\":\"HEALTHY\"}". For example, "ingress.kubernetes.io/backends": "{\"k8s-be-31224--51f3b55cd1457fb6\":\"HEALTHY\"}". The BACKEND_SERVICE_ID in this example is k8s-be-31224--51f3b55cd1457fb6.

Fetch the existing IAP settings.

gcloud iap settings get --format json \
--project=${PROJECT_ID} --resource-type=compute --service=BACKEND_SERVICE_ID > iapSettings.json

Update IapSettings with the RCToken audience.

cat iapSettings.json | jq --arg RCTOKEN_AUD_STR $RCTOKEN_AUD \
'. + {applicationSettings: {csmSettings: {rctokenAud: $RCTOKEN_AUD_STR}}}' \
> updatedIapSettings.json

gcloud iap settings set updatedIapSettings.json --format json \
--project=${PROJECT_ID} --resource-type=compute --service=BACKEND_SERVICE_ID

Enable RCToken authentication on the Istio ingress gateway.

cat <<EOF | kubectl apply -f -
apiVersion: "security.istio.io/v1beta1"
kind: "RequestAuthentication"
metadata:
  name: "ingressgateway-jwt-policy"
  namespace: "istio-system"
spec:
  selector:
    matchLabels:
      app: istio-ingressgateway
  jwtRules:
  - issuer: "https://cloud.google.com/iap"
    jwksUri: "https://www.gstatic.com/iap/verify/public_key-jwk"
    audiences:
    - $RCTOKEN_AUD
    fromHeaders:
    - name: ingress-authorization
      prefix: "Istio "
    outputPayloadToHeader: "verified-jwt"
    forwardOriginalToken: true
EOF

Optional: Ensure requests that don't have valid JWTs are rejected:

  cat <<EOF | kubectl apply -f -
  apiVersion: security.istio.io/v1beta1
  kind: AuthorizationPolicy
  metadata:
    name: iap-gateway-require-jwt
    namespace: istio-system
  spec:
    selector:
      matchLabels:
        app: istio-iap-ingressgateway
    action: DENY
    rules:
      - from:
          - source:
              notRequestPrincipals: ["*"]
  EOF

Make sure requests to the Bookinfo productpage are still successful:
```
http://DOMAIN_NAME/productpage
```

To test the policy:

Create an IapSettings request object, but set the rctokenAud to a different string:

cat iapSettings.json | jq --arg RCTOKEN_AUD_STR wrong-rctoken-aud \
'. + {applicationSettings: {csmSettings: {rctokenAud: $RCTOKEN_AUD_STR}}}' \
> wrongIapSettings.json

Call the IapSettings API to set the RCtoken audience.

gcloud beta iap settings set wrongIapSettings.json --project=PROJECT_ID --resource-type=compute --service=BACKEND_SERVICE

Make a request to the Bookinfo productpage and it should fail:
```
http://DOMAIN_NAME/productpage
```

Cleaning up

After completing this tutorial, remove the following resources to prevent unwanted charges incurring on your account:

Delete the managed certificate:

kubectl delete managedcertificates example-certificate

Delete the Ingress, which deallocates the load balancing resources:
```
kubectl -n istio-system delete ingress example-ingress
```
Delete the static IP address:
```
gcloud compute addresses delete example-static-ip --global
```
If you do this, be sure to delete the IP address from your domain registrar.
Delete the cluster, which deletes the resources that make up the cluster, such as the compute instances, disks and network resources:
```
gcloud container clusters delete CLUSTER_NAME
```