You can enable an OPA server to run as a sidecar to the Gloo external auth service. Then, you can administer an OPA server for extended use cases such as bundling. With bundling, your Rego rules can live as a signed bundle in an external, central location, such as an AWS S3 bucket to meet your internal security requirements. This sidecar approach increases the resources needed in the external auth server pod, but works better at scale and provides more OPA-native support for teams familiar with administering an OPA server. You also get the OPA-Envoy plugin API as part of the Gloo external auth service.

Other OPA options:

About the OPA sidecar

Gloo Mesh Enterprise can deploy an OPA sidecar server for you. After, you are responsible for administering the server per OPA best practices.

The following diagram and the steps in the rest of this guide show how you can set up an OPA server sidecar.

Figure: Architecture for deploying an OPA server sidecar.
Figure: Architecture for deploying an OPA server sidecar.
  1. A user sends a request that the ingress gateway receives. The request matches a route that is protected by an external auth policy that uses OPA.
  2. The ingress gateway sends the request to the external auth service for an authorization decision.
  3. The external auth service passes the request through to the OPA server sidecar to make an authorization decision.
  4. The OPA server sidecar loads the OPA config of Rego rules from a bundle in a cloud provider. The OPA server uses these Rego rules to make an authorization decision on the request. You can provide the OPA config via a YAML file during the Helm installation, or subsequently in a Kubernetes config map. Note that the request does not trigger loading the rules. You must restart the OPA server each time that you update the OPA config.
  5. The OPA server returns the authorization decision to the external auth service, which returns the authorization decision to the ingress gateway.
  6. The ingress gateway handles the request per the authorization decision.
    • If unauthorized, the ingress gateway denies the request.
    • If authorized, the ingress gateway forwards the request to the destination workload.

Clear route cache

The Envoy proxy in your sidecar instance keeps a route cache in memory of precomputed routing decisions to help speed up performance. When the sidecar gets a request, it can check the route cache to decide where to send the request. When the route cache is cleared, Gloo recomputes the routing rules. This way, any old and potentially conflicting data from the initial request is cleared.

Before you begin

  1. Complete the multicluster getting started guide to set up the following testing environment.

    • Three clusters along with environment variables for the clusters and their Kubernetes contexts.
    • The Gloo meshctl CLI, along with other CLI tools such as kubectl and istioctl.
    • The Gloo management server in the management cluster, and the Gloo agents in the workload clusters.
    • Istio installed in the workload clusters.
    • A simple Gloo workspace setup.
  2. Install Bookinfo and other sample apps.
  3. Make sure that the external auth service is installed and running. If not, install the external auth service in your Gloo environment.

      kubectl get pods --context $REMOTE_CONTEXT1  -A -l app=ext-auth-service
      
  4. Download the opa CLI tool.

Bundle Rego rules

Prepare OPA configuration for the OPA server by creating, bundling, and referring to a Rego policy with the rules you want to enforce.

  1. Create a Rego policy file in a rego directory with the rules you want to enforce with OPA. The following policy allows GET and POST HTTP requests and denies requests to the /status endpoint.

      mkdir rego
    cat <<EOF > rego/policy.rego
    package httpbin
    
    import input.http_request
    
    # deny requests by default
    default allowed = false
    
    # set allowed to true if no error message
    allowed {
        not body
    }
    
    # return result and error message
    allow["allowed"] = allowed
    allow["body"] = body
    
    # main policy logic, with error message per rule
    body = "HTTP verb is not allowed" { not http_verb_allowed }
    else = "Path is not allowed" { not path_allowed }
    
    # allow only GET and POST requests
    http_verb_allowed {
       {"GET", "POST"}[_] == http_request.method
    }
    
    # deny requests to /status endpoint
    path_allowed {
       not startswith(http_request.path, "/status")
    }
    EOF
      
  2. Create another Rego policy. The following policy uses metadata that is enabled by the OPA-Envoy plugin API. This example shows how you can use OPA to evaluate and transform responses based on request metadata.

    • Check requests for an api-key header, with valid API keys either set to the test value of test-apikey or located in data.apikeys. The API keys in data.apikeys are loaded as part of the data bundle.
    • If the request is authorized, the api-key header is removed.
    • If the request is not authorized, the body is set to Unauthorized Request and returned to the client with a 403 status code, along with a reject-reason response header.
    • In both cases, the x-response-header is added.
      cat <<EOF > rego/apikey_policies.rego
    package apikey_policies
    
    import future.keywords.if
    
    default allow := false
    
    allow {
        api_key_allowed
    }
    
    api_key_allowed {
        api_key == "test-apikey"
    }
    api_key_allowed {
        has_key(data.apikeys, api_key)
    }
    
    api_key := input.http_request.headers["api-key"]
    
    http_status := 200 {
        allow
    }
    
    http_status := 403 {
        not allow
    }
    
    body := "Unauthorized Request" {
        http_status == 403
    }
    
    headers["x-ext-auth-allow"] := "yes" if api_key_allowed
    headers["x-validated-by"] := "security-checkpoint" if api_key_allowed
    
    request_headers_to_remove := ["api-key"]
    
    response_headers_to_add["x-response-header"] := "for-client-only"
    response_headers_to_add["reject-reason"] := "unauthorized" if not allow
    
    # Helper function to check if a dictionary has a key
    has_key(dict, k) {
        dict[k]
    }
    EOF
      
  3. Use the opa CLI to bundle your Rego rules. The output of the command is a bundle.tar.gz compressed file in your current directory. For more information, see the OPA docs.

      opa build -b rego/
      
  4. Store your bundle in a supported cloud provider. For options and steps, see the OPA implementation docs.

    Example command for Google Cloud: Make sure to update the ${BUCKET_NAME} with the name of the gcs bucket.

      gsutil cp bundle.tar.gz gs://${BUCKET_NAME}/
      
  5. Create a YAML file with your OPA config. For more information, see the OPA implementation docs.

      cat > config.yaml - <<EOF
    services:
      gcs:
        url: https://storage.googleapis.com/storage/v1/b/${BUCKET_NAME}/o
    bundles:
      bundle:
        service: gcs
        resource: 'bundle.tar.gz?alt=media'
    EOF
      
    Review the following table to understand this configuration.
    SettingDescription
    servicesProvide the details of the cloud service where the bundle is located. In this example, the bundle is in a Google Cloud Storage (gcs) bucket. Make sure to update the ${BUCKET_NAME} with the name of the gcs bucket. For quick testing, you can use a bucket with a public URL. Or, you can also set up secure access with the credentials settings.
    bundlesProvide the details about the particular bundle that you want to use. In this example, the bundle is the bundle.tar.gz bundle that you previously created.
    Other settingsIf you use other features, you can configure those settings in the config map. Common settings include signed bundles and returning decision logs. For more information, see the OPA implementation docs.

Upgrade the external auth server to run the OPA sidecar

Deploy the OPA server sidecar by upgrading the external auth service in your existing Gloo Mesh Enterprise installation. You can also set up the sidecar when you first install Gloo Mesh Enterprise.

  1. Check the Helm releases in your cluster. Depending on your installation method, you either have only a main installation release (such as gloo-platform), or a main installation and a separate add-ons release (such as gloo-agent-addons), in addition to your CRDs release.

      helm ls -A --kube-context ${REMOTE_CONTEXT1} 
      
  2. Get your current installation values.

    • If you have only one release for your installation, get those values. Note that your Helm release might have a different name.

        helm get values gloo-platform -n gloo-mesh -o yaml --kube-context ${REMOTE_CONTEXT1}  > gloo-single.yaml
      open gloo-single.yaml
        
    • If you have a separate add-ons release, get those values.

        helm get values gloo-agent-addons -n gloo-mesh-addons -o yaml --kube-context ${REMOTE_CONTEXT1}  > gloo-agent-addons.yaml
      open gloo-agent-addons.yaml
        
  3. Add or edit the following settings to deploy the OPA server sidecar as part of the external auth service. For other settings, see the opaServer settings in the Helm reference docs.

      
    extAuthService:
      enabled: true
      extAuth:
        opaServer:
          enabled: true
          configYaml: ""
      
  4. Upgrade your Helm release with the OPA server sidecar. Be sure to include the OPA config file that you previously created.

    • If you have only one release for your installation, upgrade the gloo-platform release. Note that your Helm release might have a different name.

        helm upgrade gloo-platform gloo-platform/gloo-platform --kube-context ${REMOTE_CONTEXT1}  \
         --namespace gloo-mesh \
         -f gloo-single.yaml \
         --set-file configYaml=config.yaml \
         --version $GLOO_VERSION
        
    • If you have a separate add-ons release, upgrade the gloo-agent-addons release.

        helm upgrade gloo-agent-addons gloo-platform/gloo-platform --kube-context ${REMOTE_CONTEXT1}  \
         --namespace gloo-mesh-addons \
         -f gloo-agent-addons.yaml \
         --set-file configYaml=config.yaml \
         --version $GLOO_VERSION
        
  5. Verify that the external auth service is healthy, with 2 containers ready.

      kubectl get po -n gloo-mesh-addons -l app=ext-auth-service --context $REMOTE_CONTEXT1 
      
      NAME                                READY   STATUS    RESTARTS   AGE
    ext-auth-service-6546584c8d-w9s4l   2/2     Running   0          97s
      
  6. Check that the OPA server is healthy and accepted the config. Note the following example command pipes the output to jq for readability.

    • Confirm that the OPA server loaded the bundle that you referred to in the config map.
    • Confirm the health checks return a 200 response status.
    • If the OPA server is not healthy, try the OPA troubleshooting docs. Common errors include misconfiguration such as the wrong credentials to download a bundle or the wrong URL to the storage bucket.
      kubectl logs -n gloo-mesh-addons deploy/ext-auth-service -c opa-auth --context $REMOTE_CONTEXT1  | jq
      
       {
         "level": "info",
         "msg": "Bundle loaded and activated successfully. Etag updated to CMzq8eO/p4EDEAE=.",
         "name": "httpbin",
         "plugin": "bundle",
         "time": "2023-09-20T15:54:47Z"
       }
       {
         "client_addr": "@",
         "level": "info",
         "msg": "Received request.",
         "req_id": 2,
         "req_method": "GET",
         "req_path": "/health",
         "time": "2023-09-20T15:54:48Z"
       }
       {
         "client_addr": "@",
         "level": "info",
         "msg": "Sent response.",
         "req_id": 2,
         "req_method": "GET",
         "req_path": "/health",
         "resp_bytes": 3,
         "resp_duration": 0.499848,
         "resp_status": 200,
         "time": "2023-09-20T15:54:48Z"
       }
       

Create the OPA external auth policy

Create the Gloo external auth resources to enforce the OPA policy.

  1. Create an external auth server to use for your policy.

      kubectl apply --context $REMOTE_CONTEXT1  -f - <<EOF
    apiVersion: admin.gloo.solo.io/v2
    kind: ExtAuthServer
    metadata:
      name: opa-ext-auth-server
      namespace: httpbin
    spec:
      destinationServer:
        port:
          number: 8083
        ref:
          cluster: $REMOTE_CLUSTER1
          name: ext-auth-service
          namespace: gloo-mesh-addons
    EOF
      
  2. Create an external auth policy that uses the OPA config map.

  kubectl apply --context ${REMOTE_CONTEXT1} -f - <<EOF
apiVersion: security.policy.gloo.solo.io/v2
kind: ExtAuthPolicy
metadata:
  name: opa-sidecar
  namespace: httpbin
spec:
  applyToDestinations:
  - selector:
      labels:
        app: httpbin
  config:
    server:
      name: opa-ext-auth-server
      namespace: httpbin
    glooAuth:
      configs:
      - opaServerAuth:
          package: httpbin
          ruleName: allow/allowed
      - opaServerAuth:
          package: apikey_policies
EOF
  

Review the following table to understand this configuration. For more information, see the API reference.

SettingDescription
applyToDestinationsConfigure which destinations to apply the policy to, by using labels. Destinations can be a Kubernetes service, VirtualDestination, or ExternalService. If you do not specify any destinations or routes, the policy applies to all destinations in the workspace by default. If you do not specify any destinations but you do specify a route, the policy applies to the route but to no destinations.
serverThe external auth server to use for the policy.
opaServerAuthConfigure the OPA server sidecar authentication details.
packageRefer to the package in the Rego bundle that you set up in the config map earlier, such as httpbin from the policy.rego file.
ruleNameSelect the Rego rules within the bundle that you want to enforce for this OPA external auth policy.
  1. From the policy.rego file, you set the allow input document and only the allowed decision for that document, allow/allowed.
  2. For the apikey_policies.rego file, you do not set a certain rule. This way, the response has all the objects in the policy, even ones that are not used. You can take this approach with short policies like this example. However, for more complex scenarios, consult the OPA primer to create objects that you can refer to in the external auth policy.
For more information about rule names, see the OPA Data API docs.

Verify the OPA external auth policy

Verify that the Rego rules are evaluated by the OPA server and enforced by the external auth service.

  1. Confirm that the external auth policy’s state is ACCEPTED.

      kubectl get -n httpbin ExtAuthPolicy opa-sidecar -o yaml --context $REMOTE_CONTEXT1 
      
  2. Send an allowed request to the httpbin app, such as a GET bytes request with the test-apikey API key.Create a temporary curl pod in the bookinfo namespace, so that you can test the app setup. You can also use this method in Kubernetes 1.23 or later, but an ephemeral container might be simpler.

    1. Create the curl pod.
        kubectl run -it -n httpbin --context ${REMOTE_CONTEXT1} curl --image=curlimages/curl:7.73.0 --rm  -- sh
        
    2. Send a request to the ratings app.
        curl -H "X-httpbin: true" -H "api-key: test-apikey" -v http://httpbin:8000/bytes/5
        
    • In the response, you get a successful 200 status code. Also notice that the api-key header is removed and the x-response-header is added, as specified in the Rego policy.

        *   Trying 3.130.169.185:80...
      * Connected to $INGRESS_GW_IP port 80 (#0)
      > GET /bytes/5 HTTP/1.1
      > Host: www.example.com:80
      > User-Agent: curl/8.1.2
      > Accept: */*
      > X-httpbin: true
      > api-key: test-apikey
      > 
      HTTP/1.1 200 OK
      access-control-allow-credentials: true
      access-control-allow-origin: *
      content-type: application/octet-stream
      date: Thu, 16 Nov 2023 15:57:15 GMT
      content-length: 5
      x-envoy-upstream-service-time: 2
      x-response-header: for-client-only
      server: istio-envoy
      
      * Connection #0 to host $INGRESS_GW_IP left intact
      D?d?L% 
        
  3. Repeat the request, but remove the test-apikey API key. You get a 403 response because the request must meet all the Rego policy requirements to succeed.

      curl -H "X-httpbin: true" -v http://httpbin:8000/bytes/5
      

    Notice that the response includes the transformations that you specified in the Rego policy, particularly:

    • The x-response-header: for-client-only is added to the response.
    • The reject-reason: unauthorized is added to the response.
    • The body returned says Unauthorized Request.
      * Connected to $INGRESS_GW_IP port 80 (#0)
    > GET /bytes/5 HTTP/1.1
    > Host: www.example.com:80
    > User-Agent: curl/8.1.2
    > Accept: */*
    > X-httpbin: true
    
    HTTP/1.1 403 Forbidden
    reject-reason: unauthorized
    x-response-header: for-client-only
    content-length: 20
    content-type: text/plain
    date: Thu, 16 Nov 2023 15:36:05 GMT
    server: istio-envoy
    * Connection #0 to host $INGRESS_GW_IP left intact
    Unauthorized Request
      
  4. Send the request again along a path that is not allowed by the OPA policy, such as /status. Now, the request is blocked with a 404 Not Found response because the endpoint cannot be accessed.

      curl -H "X-httpbin: true" -H "api-key: test-apikey" -v http://httpbin:8000/status
      
  5. This time, send a request to an allowed endpoint but with an HTTP method that is not allowed by the OPA policy, such as PUT. The request is blocked with a 405 Method Not Allowed response.

      curl -H "X-httpbin: true" -H "api-key: test-apikey" -X PUT -v http://httpbin:8000/status
      

Cleanup

You can optionally remove the resources that you set up as part of this guide.

  1. Delete the resources that you created.
      kubectl -n gloo-mesh-addons delete ConfigMap opa-config --context $REMOTE_CONTEXT1 
    kubectl -n httpbin delete ExtAuthServer opa-ext-auth-server --context $REMOTE_CONTEXT1 
    kubectl -n httpbin delete ExtAuthPolicy opa-server --context $REMOTE_CONTEXT1 
      
  2. Repeat the Helm upgrade steps, disabling the OPA server sidecar in the external auth service in the Helm values file.
      
    extAuthService:
      enabled: true
      extAuth:
        opaServer:
          enabled: false
      

Update OPA config

To update OPA config after initially deploying the OPA server sidecar, choose from the following options.

  • Upgrade your Helm installation with the new OPA config.
  • Create a Kubernetes config map with the new OPA config and restart the OPA server, as show in the following steps.

Steps for creating and updating config maps:

  1. Follow Steps 1 - 3 of Bundle Rego rules to create, bundle, and store your Rego rules in a cloud provider.

  2. Create a Kubernetes config map that refers to your bundle.

      kubectl apply --context $REMOTE_CONTEXT1  -f - <<EOF
    apiVersion: v1
    kind: ConfigMap
    metadata:
      name: opa-config
      namespace: gloo-mesh-addons
    data:
      config.yaml: |
        services:
          gcs:
            url: https://storage.googleapis.com/storage/v1/b/${BUCKET_NAME}/o
        bundles:
          bundle:
            service: gcs
            resource: 'bundle.tar.gz?alt=media'
    EOF
      
    Review the following table to understand this configuration.
    SettingDescription
    namespaceCreate the config map in the same namespace as the external auth server, such as gloo-mesh-addons.
    config.yamlEnter the bundle configuration details that you created as part of uploading your bundle to the cloud provider. For more information, see the OPA implementation docs.
    servicesProvide the details of the cloud service where the bundle is located. In this example, the bundle is in a Google Cloud Storage (gcs) bucket. Make sure to update the ${BUCKET_NAME} with the name of the gcs bucket. For quick testing, you can use a bucket with a public URL. Or, you can also set up secure access with the credentials settings.
    bundlesProvide the details about the particular bundle that you want to use. In this example, the bundle is the bundle.tar.gz bundle that you previously created.
    Other settingsIf you use other features, you can configure those settings in the config map. Common settings include signed bundles and returning decision logs. For more information, see the OPA implementation docs.
  3. For your OPA config changes to take effect, restart the external auth service with the OPA server sidecar. You must restart the OPA server each time that you update the OPA config. Optionally, you can create the config map before enabling the OPA server sidecar and refer to the config map during the Helm installation. This way, the first time the OPA server sidecar comes up, it has the OPA config already, reducing the number of times you might have to restart the service.

      kubectl rollout restart deployment/ext-auth-service -n gloo-mesh-addons --context $REMOTE_CONTEXT1 
      
  4. Optional: Check that the OPA server is healthy and accepted the config. Note the following example command pipes the output to jq for readability.

    • Confirm that the OPA server loaded the bundle that you referred to in the config map.
    • Confirm the health checks return a 200 response status.
      kubectl logs -n gloo-mesh-addons deploy/ext-auth-service -c opa-auth --context $REMOTE_CONTEXT1  | jq
      
       {
         "level": "info",
         "msg": "Bundle loaded and activated successfully. Etag updated to CMzq8eO/p4EDEAE=.",
         "name": "httpbin",
         "plugin": "bundle",
         "time": "2023-09-20T15:54:47Z"
       }
       {
         "client_addr": "@",
         "level": "info",
         "msg": "Received request.",
         "req_id": 2,
         "req_method": "GET",
         "req_path": "/health",
         "time": "2023-09-20T15:54:48Z"
       }
       {
         "client_addr": "@",
         "level": "info",
         "msg": "Sent response.",
         "req_id": 2,
         "req_method": "GET",
         "req_path": "/health",
         "resp_bytes": 3,
         "resp_duration": 0.499848,
         "resp_status": 200,
         "time": "2023-09-20T15:54:48Z"
       }