Configuring Anthos Service Mesh user authentication

Preview

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Anthos 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 Anthos 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. Anthos 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, Anthos Service Mesh enforces Istio authorization policies, and on successful authorization, it transmits the identity to workloads in a secure credential format.

How it works

Anthos 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 an Anthos 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 Anthos 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

Ensure that you meet the prerequisites by using the following steps.

Customize the installation using the user authentication overlay

To install the user authentication service, you must customize the ASM installation to add a mesh level external authorization provider.

1. Get the example user auth overlay and update it if there are any customizations in your mesh. It is a recommended best practice to maintain this overlay file in your source control.

   curl https://raw.githubusercontent.com/GoogleCloudPlatform/asm-user-auth/release-0.1/overlay/user-auth-overlay.yaml > user-auth-overlay.yaml
   

2. Follow the install ASM with overlay to use a Google-provided script to install Anthos Service Mesh with the user authentication overlay. For example:

   /install_asm \
    --project_id "PROJECT_ID" \
    --cluster_name "CLUSTER_NAME" \
    --cluster_location "CLUSTER_LOCATION" \
    --mode install \
    --enable_all \
    --custom_overlay user-auth-overlay.yaml
   

   Important: If you customize the installation with multiple overlays, ensure the --custom_overlay option includes all your overlay files.

   The user authentication kpt packages creates an AuthorizationPolicy to reference the external authorization provider specified by pkg/ext-authz.yaml.

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://localhost:8443/_gcp_anthos_callback.

   Then, click Save.

3. In addition, save your client ID and client secret to use later:

   export OIDC_CLIENT_ID='<your-client-id>'
   export OIDC_CLIENT_SECRET='<your-client-secret>'
   export OIDC_ISSUER_URI='https://accounts.google.com'
   

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.

1. Get the kpt package:

   kpt pkg get https://github.com/GoogleCloudPlatform/asm-user-auth@release-0.1 .
   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. A production deployment should not use self-signed certificates.

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 istio-system 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 the these keys instead.

1. After you generate your keys, put the key data in the same format:

   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
        }
     ]
   }
   

   cat ./samples/cookie_encryption_key.json
   {
     "keys":[
        {
           "kty":"oct",
           "kid":"key-0",
           "K":"YOUR_KEY",
           "useAfter": 1612813735
        }
     ]
   }
   

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

   Important: In a production environment, generate your own keys to populate the JSON file instead.

   kubectl create namespace asm-user-auth
   kubectl label namespace asm-user-auth  istio-injection=enabled istio.io/rev=default --overwrite
   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.

1. Set the oauth variables:

   kpt cfg set pkg anthos.servicemesh.user-auth.oidc.clientID ${OIDC_CLIENT_ID}
   kpt cfg set pkg anthos.servicemesh.user-auth.oidc.clientSecret ${OIDC_CLIENT_SECRET}
   kpt cfg set pkg anthos.servicemesh.user-auth.oidc.issuerURI ${OIDC_ISSUER_URI}
   

2. Apply the kpt package:

   kubectl apply -f ./pkg/asm_user_auth_config_v1alpha1.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. It contains these fields:

cat pkg/user_auth_config.yaml

apiVersion: security.anthos.io/v1alpha1
kind: UserAuthConfig
metadata:
  name: auth-config
  namespace: user-auth
spec:
  authentication:
  - oidc:
      clientID: "${OIDC_CLIENT_ID}"
      clientSecret: "${OIDC_CLIENT_SECRET}"
      issuerURI: "${OIDC_ISSUER_URI}"
      redirectURIHost: ""
      redirectURIPath: "/_gcp_anthos_callback"
  outputJWTAudience: "test_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 Online Boutique sample application as an example.

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

The installation process also creates an Istio gateway to serve HTTPS traffic using the TLS certificate userauth-tls-cert you created above. Here is the pkg/gateway.yaml configuration.

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: /_gcp_anthos_callback
    name: user-auth-route
    route:
    - destination:
        host: authservice
        port:
          number: 10004

1. Update the Online Boutique application to use this gateway to serve HTTPS traffic, and use port forwarding to access the application locally:

   kubectl apply -f./samples/boutique-route.yaml -n demo
   kubectl port-forward service/istio-ingressgateway 8443:443 -n istio-system
   

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

2. Verify that the Online Boutique sample application is accessible at https://localhost:8443/.

Verify user authentication

The Online Boutique application services now require the end user to login via their Google accounts.

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

2. After you login, click Next and verify that it redirects you to the Online Boutique home 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/rctoken-authz.yaml
   

2. The rctoken-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: RequestAuthentication
   metadata:
    name: require-rc-token
    namespace: istio-system
   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
    namespace: istio-system
   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
   

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 tokenEndpoint and authorizationEndpoint configured in the UserAuthConfig CRD has a route configured in VirtualService. The previous installation steps set this in asm-user-auth/userauth-oidc VirtualService.

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
      }
   ]
}

Anthos 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.

User authentication configuration details

The following table describes each field in the CRD:

Field name	Description
authentication.oidc	This section holds the OIDC endpoint configuration and the parameters used in OIDC flow.
authentication.oidc.certificateAuthorityData	This is the SSL certificate of the domain of the OIDC authorization server.
authentication.oidc.clientID	The OAuth client ID to use for the OIDC authentication flow.
authentication.oidc.clientSecret	The OAuth client secret to use for the OIDC authentication flow.
authentication.oidc.issuerURI	The URI to use as the issuer in the output RCToken.
authentication.oidc.redirectURIHost	The host to be used for OAuth termination URI. If you leave this empty, the host from the target URL will be used and the redirect URI will be assembled dynamically. This value can be used when a user auth SSO session is desired at a higher level domain. For example, to enable SSO between profile.example.com/ and admin.example.com/, this value can be set to example.com. It will enable a user auth session to be established at example.com that'll be shared amongst all subdomains. Note: If multiple domains are served from the same mesh, example1.com and example2.com, the feature cannot be used, and is recommended to be left empty.
authentication.oidc.redirectURIPath	The endpoint path where `authservice` will terminate the OAuth flow. You should register this URI path plus the host as an authorized redirect URI in the authorization server for the authentication.oidc.clientID. In addition, this URI should be served from the same service mesh and ingress where `authservice` is enabled.
authentication.oidc.scopes	The OAuth scope that should be requested in the authentication request.
authentication.oidc.groupsClaim	If the `idtoken` contains a groups claim, use this field to indicate its name. If specified, the service will pass on the data in this claim into the `groups` claim in the output RCToken.
authentication.outputJWTAudience	The audience of the RCToken generated by `authservice`. The sidecars can validate the incoming RCToken against this audience value.

Multi Cluster Deployment

Anthos 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.

FAQs

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

   Follow the Anthos Service Mesh upgrade process and specify the user-auth.yaml overlay file on the command line to install_asm.