Configuring Cloud Service Mesh user authentication

If you have the TRAFFIC_DIRECTOR control plane implementation then this feature is only supported by allow-list. Please contact support to request this feature be allowlisted for your organization

Cloud Service Mesh user authentication is an integrated solution for browser-based end-user authentication and access control to your deployed workloads. It lets you integrate with existing Identity Providers (IDP) for user authentication and uses Istio APIs and authorization policies for access management. It is a user-friendly alternative to Istio JSON Web Token (JWT) authentication.

A typical use-case is when an organization uses Cloud Service Mesh to host a web application for its workforce to access via a web browser. In addition, the organization needs to use their existing identity provider to manage user identities. Cloud Service Mesh user authentication makes it easy for users to authenticate using a standard web-based OpenID Connect (OIDC) login and consent flow. When the user authenticates, Cloud Service Mesh enforces Istio authorization policies, and on successful authorization, it transmits the identity to workloads in a secure credential format.

How it works

Cloud Service Mesh user authentication introduces a new component, authservice. This component integrates with the Envoy-based ingress as an external authorization service that intercepts all the incoming requests for authentication. authservice implements the client-side of the OIDC protocol and enables user access to applications via a browser, where users complete an interactive authentication and consent flow to establish a short-lived session. authservice implements industry standard protocols to integrate with any identity provider that can act as a OIDC authorization server. When the user is authenticated, the principal information is encapsulated in an RCToken in JWT format, signed by authservice which it forwards to the Istio authorization layer in the ingress. This model provides perimeter access control for traffic into the mesh. If the user is authorized to access a resource, this RCToken is also forwarded to the microservices to obtain principal information and enforce fine-grained access control.

The following diagram shows the location of authservice in the mesh and how it relates to the other parts of the mesh, such as the ingress, workloads, user's browser, and any existing IDP.

Administrators can install authservice as an add-on over a Cloud Service Mesh installation. When installed, authservice reads the OIDC endpoint configuration and other associated settings defined in the UserAuth custom resource. The administrator can use Cloud Service Mesh ExternalAuthorization APIs to configure auth_server as a filter on the ingress.

Install the user authentication service

The following steps explain how to configure the authservice.

Prerequisites

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

• If you are using managed Cloud Service Mesh on a private cluster, then ensure the cluster is capable of sending egress traffic to the IDP.

Additionally, ensure that you meet the prerequisites by using the following steps.

Customize the installation user authentication overlay

To install the user authentication service, you must customize the Cloud Service Mesh installation to add a mesh-level external authorization provider. The steps required depend on whether you are using managed or in-cluster Cloud Service Mesh.

Prepare the OIDC client configuration

Set your OIDC client configuration by using the following steps. This guide uses Google as an IDP, but you can use any IDP that supports OIDC authentication.

1. In the Google Cloud console, go to API & Services > Credentials.

   Go to Credentials

2. Go to Create Credentials, then choose OAuth client ID. If required, set your OAuth consent screen options, then configure the following options:

   • Set Application type to Web application.
   • Set Authorized redirect URI to https://REDIRECT_HOST/REDIRECT_PATH. For example, for localhost you could set to https://localhost:8443/_gcp_asm_authenticate.

   Then, click Save.

3. In addition, save your OIDC client configuration to use later.

   export OIDC_CLIENT_ID=CLIENT_ID
   export OIDC_CLIENT_SECRET=CLIENT_SECRET
   export OIDC_ISSUER_URI=ISSUER_URI
   export OIDC_REDIRECT_HOST=REDIRECT_HOST
   export OIDC_REDIRECT_PATH=REDIRECT_PATH
   

Get the kpt packages

Use the following steps to install the recommended authservice configuration from the public repository. These commands retrieve the latest authservice container and start it as a Pod in the asm-user-auth namespace. It also configures the ingress to intercept all requests.

Get the kpt package:

kpt pkg get https://github.com/GoogleCloudPlatform/asm-user-auth.git/@v1.2.3 .
cd asm-user-auth/

Set the redirection URL and secret for ingress gateway

OAuth2 requires a redirection URL hosted on an HTTPS-protected endpoint. These commands are for example purposes and simplify setup by generating a self-signed certificate for the Istio ingress gateway.

1. Generate a self-signed certificate:

   openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem \
    -days 365 -nodes -subj '/CN=localhost'
   

2. Create a secret for the ingress gateway to host HTTPS traffic:

   kubectl create -n asm-user-auth secret tls userauth-tls-cert --key=key.pem \
   --cert=cert.pem
   

Apply the encryption and signing keys

The authservice needs two sets of keys to operate successfully. The first is a symmetric key for encryption and decryption. This key is used for encrypting the session state before setting that as a cookie.

The second set of keys are a public/private key pair. This key is used to sign the authenticated user information in JWT format as an RCToken. The public key from this pair is published at a predefined endpoint that the sidecars can use to validate the JWT.

The user authentication kpt package contains two sample keys for quick setup. However, you can use your preferred key management system to generate these keys instead.

1. Prepare the session encryption key with following format or use the sample from the pkg, which you can view by cat ./samples/cookie_encryption_key.json.

   {
     "keys":[
        {
           "kty":"oct",
           "kid":"key-0",
           "K":"YOUR_KEY",
           "useAfter": 1612813735
        }
     ]
   }
   

   You can generate a test AES key with following command:

   openssl enc -aes-256-cbc -k mycustomkey -P -md sha1 | grep key
   

2. Prepare the RCToken signing key with following format or use the sample from the pkg, which you can view by cat ./samples/rctoken_signing_key.json.

   {
     "keys":[
        {
           "kty":"RSA",
           "kid":"rsa-signing-key",
           "K":"YOUR_KEY",  # k contains a Base64 encoded PEM format RSA signing key.
           "useAfter": 1612813735  # unix timestamp
        }
     ]
   }
   

   You can generate a test 256-bit RSA private key with following command:

   openssl genpkey -algorithm RSA -out rsa_private.pem -pkeyopt rsa_keygen_bits:256
   

3. Create the kubernetes secret, which authservice will mount into its own file system.

   kubectl create secret generic secret-key  \
       --from-file="session_cookie.key"="./samples/cookie_encryption_key.json" \
       --from-file="rctoken.key"="./samples/rctoken_signing_key.json"  \
       --namespace=asm-user-auth
   

Deploy the user authentication service

The following commands create the user authentication service and deployment in the asm-user-auth namespace.

Set the necessary values for User Auth configuration. The client ID and secret are stored as Kubernetes secrets, so we use Base64 to encode them. Please visit public repository to view all available setters.

kpt fn eval pkg --image gcr.io/kpt-fn/apply-setters:v0.2 --truncate-output=false -- \
  client-id="$(echo -n ${OIDC_CLIENT_ID} | base64 -w0)" \
  client-secret="$(echo -n ${OIDC_CLIENT_SECRET} | base64 -w0)" \
  issuer-uri="${OIDC_ISSUER_URI}" \
  redirect-host="${OIDC_REDIRECT_HOST}" \
  redirect-path="${OIDC_REDIRECT_PATH}"

Apply the kpt package:

# Remove the potential alpha version CRD if exists.
kubectl delete crd userauthconfigs.security.anthos.io
kubectl apply -f ./pkg/asm_user_auth_config_v1beta1.yaml
kubectl apply -f ./pkg

The authservice consumes the UserAuthConfig CRD to provide end user authentication. UserAuthConfig is configurable in the run time, and you can update it to change the authservice behavior and configure it with endpoints for any OIDC authorization server.

You can view the file by cat pkg/user_auth_config.yaml, it contains these fields:

apiVersion: security.anthos.io/v1beta1
kind: UserAuthConfig
metadata:
  name: user-auth-config
  namespace: asm-user-auth
spec:
  authentication:
    oidc:
      certificateAuthorityData: ""  # kpt-set: ${ca-cert}
      issuerURI: "<your issuer uri>"  # kpt-set: ${issuer-uri}
      proxy: ""  # kpt-set: ${proxy}
      oauthCredentialsSecret:
        name: "oauth-secret"  # kpt-set: ${secret-name}
        namespace: "asm-user-auth"  # kpt-set: ${secret-namespace}
      redirectURIHost: ""  # kpt-set: ${redirect-host}
      redirectURIPath: "/_gcp_asm_authenticate"  # kpt-set: ${redirect-path}
      scopes: ""  # kpt-set: ${scopes}
      groupsClaim: ""  # kpt-set: ${groups}
  outputJWTAudience: "test_audience"  # kpt-set: ${jwt-audience}

See user authentication configuration details for detailed descriptions of the user_auth_config.yaml fields.

Perform post-install tasks

The following tasks are required after you finish the previous installation steps.

Enable user authentication for your applications

This section demonstrates how to enable user authentication, by using the httpbin as an example.

Cloud Service Mesh user authentication uses a CUSTOM typed authorization policy to trigger the OIDC flow.

After you have installed the Istio gateway, configure it to serve HTTPS traffic using the TLS certificate userauth-tls-cert you created above. Below is the pkg/gateway.yaml configuration that you just installed.

apiVersion: networking.istio.io/v1beta1
kind: Gateway
metadata:
  name: userauth
  namespace: asm-user-auth
spec:
  selector:
    istio: ingressgateway
  servers:
  - hosts:
    - '*'
    port:
      name: https
      number: 443
      protocol: HTTPS
    tls:
      mode: SIMPLE
      credentialName: userauth-tls-cert
---
# This ensures the OIDC endpoint has at least some route defined.
apiVersion: networking.istio.io/v1beta1
kind: VirtualService
metadata:
  name: userauth-oidc
  namespace: asm-user-auth
spec:
  gateways:
  - userauth
  hosts:
  - '*'
  http:
  - match:
    - uri:
        prefix: /status
    - uri:
        prefix: "your-oidc-redirect-path"
    name: user-auth-route
    route:
    - destination:
        host: authservice
        port:
          number: 10004

1. Label default namespace to enable istio-proxy auto injection for deployments.

   kubectl label namespace default istio.io/rev=REVISION --overwrite
   

2. Deploy httpbin to default namespace.

   kubectl apply -f https://raw.githubusercontent.com/istio/istio/master/samples/httpbin/httpbin.yaml -n default
   

3. Update httpbin to use this gateway to serve HTTPS traffic, and use port forwarding to access the application locally:

   kubectl apply -f./samples/httpbin-route.yaml -n default
   kubectl port-forward service/istio-ingressgateway 8443:443 -n asm-user-auth
   

   apiVersion: networking.istio.io/v1alpha3
   kind: VirtualService
   metadata:
     name: httpbin
     namespace: default
   spec:
     gateways:
     - asm-user-auth/userauth
     hosts:
     - '*'
     http:
     - match:
       - uri:
           prefix: /ip
       - uri:
           prefix: /headers
       name: httpbin-routes
       route:
       - destination:
           host: httpbin.default.svc.cluster.local
           port:
             number: 8000
   

   The ingress gateway on port 8443 will be forwarded to localhost to make the application accessible locally.

4. Deploy the samples/rctoken-authz.yaml to enable RequestAuthentication and AuthorizationPolicy to verify the RCToken for the requests.

   kubectl apply -f ./samples/rctoken-authz.yaml -n asm-user-auth
   

   Example samples/rctoken-authz.yaml:

   apiVersion: security.istio.io/v1beta1
   kind: RequestAuthentication
   metadata:
     name: require-rc-token
   spec:
     selector:
       matchLabels:
         istio: ingressgateway
     jwtRules:
     - issuer: "authservice.asm-user-auth.svc.cluster.local"
       audiences:
       - "test_audience"
       jwksUri: "http://authservice.asm-user-auth.svc.cluster.local:10004/_gcp_user_auth/jwks"
       fromHeaders:
       - name: X-ASM-RCTOKEN
       forwardOriginalToken: true
   ---
   apiVersion: security.istio.io/v1beta1
   kind: AuthorizationPolicy
   metadata:
     name: require-rc-token
   spec:
     selector:
       matchLabels:
         istio: ingressgateway
     action: ALLOW
     rules:
     - when:
       - key: request.auth.claims[iss]
         values:
         - authservice.asm-user-auth.svc.cluster.local
       - key: request.auth.claims[aud]
         values:
         - test_audience
   

Verify user authentication

The httpbin serves two paths, /ip is publicly accessible and /headers requires the end user to login via their configured IDP.

1. Verify that you are able to access /ip directly by visiting https://localhost:8443/ip.

2. Verify that you see the OIDC login page by visiting https://localhost:8443/headers.

3. After you login, click Next and verify that it redirects you to the /headers page.

Configure authorization policies

After you finish the configuration in the previous steps, each user will be redirected through a web-based authentication flow. When the flow completes, the authservice will generate an RCToken in JWT format, which it uses to transmit the authenticated user information.

1. Add Istio authorization policies at the ingress to ensure that an authorization check occurs for each authenticated user:

   kubectl apply -f ./samples/httpbin-authz.yaml -n asm-user-auth
   

2. The httpbin-authz.yaml file configures the ingress gateway to validate the RC token issued by authservice, and only authorize when the JWT contains the desired fields, such as audiences and issuers.

   See the following example authorization policy:

   apiVersion: security.istio.io/v1beta1
   kind: AuthorizationPolicy
   metadata:
     name: require-rc-token
   spec:
     selector:
       matchLabels:
         istio: ingressgateway
     action: ALLOW
     rules:
     - to:
       - operation:
           paths: ["/ip"]
     - to:
       when:
       - key: request.auth.claims[iss]
         values:
         - authservice.asm-user-auth.svc.cluster.local
       - key: request.auth.claims[aud]
         values:
         - test_audience
       - key: request.auth.claims[sub]
         values:
         - allowed_user_sub_1  # Change this with the "sub" claim in the RC token. Wildcard '*' will match everything.
   

Configure environment-specific settings

The previous steps use localhost and a self-signed HTTPS certificate for quick setup. For real production use, use your own domain, such as example.com.

In addition, ensure the certificateAuthorityData has the intended root cert content. For example, if the IDP is trusted with system's root certs, you can leave it empty. If there is a HTTPS proxy terminating the HTTPS connection, it should be set to the proxy's root cert.

Manage and rotate keys

There are two sets of keys used by authservice. You can rotate each key independently. However, before you rotate the keys, it is important to understand how the rotation works.

Both keys are in JSON format. The useAfter field specifies the timestamp since when the key will be considered to use. During a key rotation, you should include both old and new keys in the JSON. For example, in the following example, new-key will only be used after timestamp 1712813735.

{
   "keys":[
      {
         "kty":"RSA",
         "kid":"old-key",
         "K":"...", # k contains a Base64 encoded PEM format RSA signing key.
         "useAfter": 1612813735, # unix timestamp
      }
      {
      "kty":"RSA",
         "kid":"new-key",
         "K":"...", # k contains a Base64 encoded PEM format RSA signing key.
         "useAfter": 1712813735, # unix timestamp
      }
   ]
}

Cloud Service Mesh uses the symmetric key for encrypting session data that is stored in browser cookies. To ensure validity of existing sessions, authservice attempts decryption with all keys in the key set. On rotation, the authservice will use the new key for encrypting new sessions, and will continue to attempt decryption with the old keys.

The public/private key pair is used to sign RCToken. The public key is transmitted to the sidecars by istiod for JWT verification. It is crucial for sidecars to receive the new public key before authservice starts using the new private key to sign the RCToken. To that end, authservice starts publishing the public key immediately after the key is added, but waits a significant amount of time before starting to use that to sign RCToken.

To summarize, when performing key rotations we recommend:

1. Perform regular key rotations or on demand as you need.
2. In the JSON format, include both the current and the new keys. The new keys should be associated with a timestamp in the future. We recommend that you specify a timestamp at least a couple of hours ahead of the current time.
3. Monitor and confirm that the services are still healthy after the new key is in use. Wait at least one day after the new key is being used before moving to next step.
4. Remove the old keys from the JSON entries. They are no longer needed.

Multi Cluster Deployment

Cloud Service Mesh User Auth supports multi cluster deployment. You need to deploy user auth in each cluster as described above. The user auth configuration such as UserAuth custom resource, OIDC client secret, encryption keys, all need to be replicated in each clusters.

By default ingress gateway will load balance the authentication requests to any one of authservice instances. You can use destination rule to configure the ingress gateway to send requests to the authservice in the same cluster, and only fail over to other clusters' authservice.

apiVersion: networking.istio.io/v1beta1
kind: DestinationRule
metadata:
  name: authservice-fail-over
  namespace: asm-user-auth
spec:
  host: authservice.asm-user-auth.svc.cluster.local
  trafficPolicy:
    loadBalancer:
      localityLbSetting:
        enabled: true
        failover:
        - from:  us-east
          to: us-west
        - from: us-west
          to: us-east

Same as other configuration, this needs to be configured in each cluster.

Custom claims mapping

To configure custom claims mapping, configure spec.authentication.oidc.attributeMapping to define any mappings from original identity provider's IDToken. The key will be the claim name in the RCToken and value is a CEL expression on how to parse the claim from IDToken, use assertion to reference the IDToken.

Example:

spec:
  authentication:
    oidc:
      attributeMapping:
        aud_copy: assertion.aud
        decision: 'assertion.sub.startsWith("123") ? "success" : "fail"'

In the RCToken, a nested claim attributes contains the claims that been configured:

"attributes": {
    "aud_copy": "foo.googleusercontent.com",
    "decision": "success"
}

If the CEL expression fails to parse the value from IDToken, it will ignore the claim without failing the authentication flow.

User Auth upgrades

1. Install the user-auth packages again as it contains the updated binary for new user-auth version:

   kpt pkg get https://github.com/GoogleCloudPlatform/asm-user-auth.git/@v1.2.3 .
   cd asm-user-auth/
   

2. Save your OIDC client configuration:

   export OIDC_CLIENT_ID=CLIENT_ID
   export OIDC_CLIENT_SECRET=CLIENT_SECRET
   export OIDC_ISSUER_URI=ISSUER_URI
   export OIDC_REDIRECT_HOST=REDIRECT_HOST
   export OIDC_REDIRECT_PATH=REDIRECT_PATH
   

3. Deploy the user authentication service to upgrade to a new version.

User authentication configuration details

The following table describes each field in the CRD:

Troubleshoot

1. Network accessibility to IDP.

   Possible log: error: TLS handshake failed..

   Verify by executing curl from the ephemeral container attached to the istio-proxy to call IDP issuer URI. For example, see Collecting Cloud Service Mesh logs.

   If you're unable to connect, check the firewall rules or other network configurations for the cluster.

2. Root CA certificate.

   Possible log: error: The server's TLS certificate did not match expectations. or error: TLS handshake failed..

   Make sure the certificateAuthorityData holds the correct root CA certificate. When there is no HTTPS proxy terminating HTTPS traffic, this should hold the root CA certificate for the IDP. If there is one, this should hold the proxy's instead.

3. Redirect path configuration.

   Possible observation: receive 404 error page during OIDC authentication flow.

   User Auth returns the "Set-Cookie" header without using the path attribute, which by default the browser uses the directory of the request url as the cookie path (scope of the cookie related to path). So we recommend to not include "/" in the redirect path unless you are intended.

4. The sidecar is not able to fetch jwksUri.

   In some scenarios, a sidecar restriction could lead to failure of fetching jwksUri. If the namespace is not present using a wildcard (for example, ./* or istio-system/*) then this will not work. You must manually add their namespace in the egress sidecar.

FAQs

1. How do I upgrade Cloud Service Mesh with User Auth enabled?

   Follow the Cloud Service Mesh upgrade process and specify the overlay file by adding --custom_overlay user-auth-overlay.yaml on the command line to asmcli install.

2. How much resources should we provision for the authservice? And how many requests per second can it handle?

   By default, authservice is configured with 2.0 vCPU, 256Mi memory. Under such configuration, authservice is able to handle 500 requests per second. To handle larger amounts of requests, you should provision more CPU, which is roughly proportionally to its requests handling capacity. You can also configure multiple replicas of the authservice to increase the horizontal scalability.