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

• Install required tools
• Download asmcli
• Grant cluster admin permissions
• Validate your project and cluster

Additionally, this guide assumes that you have:

• A Google Cloud project.
• A Cloud Billing account.

Setting up a cluster with Anthos Service Mesh

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

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.

1. Reserve a static external IP address:

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

2. Get the static IP address:

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

3. 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

1. 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
   

2. 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.

   • 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

1. 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]
   

2. 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.

1. 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

2. 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

3. 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}'
   

4. 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

5. 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.

1. 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:

1. Create an environment variable for the RCToken audience. This can be any string that you want.

   export RCTOKEN_AUD="your-rctoken-aud"
   

2. 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.

3. Fetch the existing IAP settings.

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

4. 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
   

5. 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
   

6. 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
     

7. Make sure requests to the Bookinfo productpage are still successful:

   http://DOMAIN_NAME/productpage

To test the policy:

1. 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
   

2. 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

3. 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:

1. Delete the managed certificate:

   kubectl delete managedcertificates example-certificate

2. Delete the Ingress, which deallocates the load balancing resources:

   kubectl -n istio-system delete ingress example-ingress

3. 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.

4. 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