Skip to main content
Mapagam

Implementing External Authorization

1. Understanding External Authorization

Aspect Description Details
Authorization Model Defines how access control is enforced External authorization allows policy enforcement outside the service mesh, typically using a dedicated authorization service or API.
Policy Enforcement Point (PEP) Location where authorization checks occur In service mesh, PEPs are typically located at the sidecar proxies (e.g., Envoy) or at the ingress gateways.
Authorization Service External system enforcing policies Can be a dedicated service like OPA (Open Policy Agent), Istio's AuthorizationPolicy, or custom RBAC services.
Request Context Data used for authorization decisions Includes headers, source/destination identities, HTTP methods, paths, and custom claims from JWT tokens.
Decision Types Authorization outcomes Allow or deny access, with optional logging and metrics capture for auditing.

Example: Authorization Policy in Istio

apiVersion: security.istio.io/v1
kind: AuthorizationPolicy
metadata:
  name: external-authz
spec:
  action: ALLOW
  rules:
  - from:
    - source:
        principals: ["cluster.local/ns/default/sa/authz-service"]
    to:
    - operation:
        methods: ["GET"]
        paths: ["/api/public/*"]
Note: External authorization is useful for implementing fine-grained access control policies that are not easily expressed within the service mesh's built-in authorization models.

2. Configuring HTTP External Authorization

Property Value Description
authz.http.host authz.example.com Host of the external authorization service
authz.http.port 9000 Port of the external authorization service
authz.http.path /authorize Path to the authorization endpoint
authz.http.timeout 1s Timeout for the authorization request
authz.http.tls.enabled false Enable TLS for the authorization request

Example: HTTP Authorization Configuration

authorization:
  http:
    host: authz.example.com
    port: 9000
    path: /authorize
    timeout: 1s
    tls:
      enabled: false
Note: The external authorization service must respond to the /authorize endpoint with a 200 OK for allow or 403 Forbidden for deny.

3. Configuring gRPC External Authorization

Property Description Value
grpc_service gRPC service configuration for external authorization { "host": "authz-service.default.svc.cluster.local", "port": 9000 }
timeout Timeout for gRPC authorization call 100ms
fail_open Whether to allow requests when authorization service is unavailable false

Example: gRPC Authorization Service Configuration

authorization:
  grpc_service:
    host: authz-service.default.svc.cluster.local
    port: 9000
  timeout: 100ms
  fail_open: false
Note: The gRPC service must implement the Authorization interface defined in the Envoy external authorization API.

4. Setting Authorization Headers

Header Name Value Format Description Usage
Authorization Bearer <token> Token for authentication Used to pass JWT or other tokens
X-Forwarded-User <username> Original user identity Passed through when proxying requests
X-Forwarded-Groups <group1>,<group2> Groups the user belongs to Used for role-based access control

Example: Setting Authorization Headers in Envoy

filters:
  - name: envoy.filters.http.ext_authz
    typed_config:
      "@type": type.googleapis.com/envoy.extensions.filters.http.ext_authz.v3.ExtAuthz
      service:
        grpc_service:
          envoy_grpc:
            cluster_name: auth_server
      authorization_request:
        headers_to_add:
          - key: "Authorization"
            value: "Bearer {token}"
          - key: "X-Forwarded-User"
            value: "{user}"
Note: Ensure that the authorization headers are properly sanitized to prevent header injection attacks.

5. Configuring Authorization Body

Property Description Values Notes
authorizationBody Defines the structure of the authorization request body string Used in conjunction with authorizationRequest to define the body content for authorization checks
authorizationBody.path Path to the authorization body in the request string Can be used to extract authorization data from a nested field in the request body
authorizationBody.method HTTP method to use when sending the authorization request GET, POST, PUT, DELETE Defaults to POST if not specified
authorizationBody.headers Headers to include in the authorization request object Key-value pairs of header names and values to be sent with the authorization request

Example: Authorization Body Configuration

authorization:
  body:
    path: /auth
    method: POST
    headers:
      Content-Type: application/json

6. Implementing Authorization Caching

Property Description Default Value Notes
cache.enabled Enables or disables the authorization cache false Set to true to enable caching
cache.ttl Time-to-live for cached authorization decisions 30s Duration after which cached entries expire
cache.size Maximum number of entries in the cache 1000 Adjust based on expected authorization load

Example: Enabling Authorization Caching

authorization:
  cache:
    enabled: true
    ttl: 60s
    size: 2000
Note: Caching can improve performance but may introduce staleness in authorization decisions.
Warning: Ensure cache invalidation is handled correctly to avoid stale permissions.

7. Managing Authorization Timeouts

Property Values Description
authorization.timeout 30s Timeout for authorization requests to external services
authorization.retryAttempts 3 Number of retry attempts on authorization timeout
authorization.retryBackoff 100ms Backoff time between retry attempts

Example: Authorization Timeout Configuration

authorization:
  timeout: 30s
  retryAttempts: 3
  retryBackoff: 100ms
Note: Setting timeout too low may cause authorization failures during high load. Adjust based on your external auth service response times.

8. Configuring Authorization Failure Mode

Mode Description Behavior Default
deny Deny all requests that fail authorization All unauthorized requests are rejected with a 403 status NEW
allow Allow all requests regardless of authorization status All requests are permitted, even if unauthorized Legacy behavior (deprecated)
deny_unknown Deny requests when authorization status is unknown Requests with unclear auth state are rejected Stable

Example: Authorization Failure Mode Configuration

authorization:
  failureMode: deny
  policies:
    - name: "allow-read-only"
      rules:
        - path: "/api/v1/data"
          methods: ["GET"]
Note: The deny_unknown mode is recommended for production environments to ensure strict access control.

9. Implementing Custom Authorization Logic

Property Description Example
authz.policy Defines the custom authorization policy to enforce allow: user.role == 'admin'
authz.context Context variables passed to the authorization engine { user: 'alice', resource: '/api/v1/users' }

Example: Custom Policy Implementation

const policy = {
  allow: (context) => {
    return context.user.role === 'admin' || context.resource.startsWith('/api/v1/public');
  }
};
Note: Custom authorization logic should be evaluated before any resource access to prevent unauthorized actions.
Warning: Misconfigured custom policies can lead to security vulnerabilities. Always validate and test policies in a staging environment.

10. Troubleshooting External Authorization

Common Issues and Solutions

  1. Authorization Denied: Check if the client is sending the correct headers or tokens. Ensure that the external authorization service is correctly configured to accept and process these credentials.
  2. Timeouts: If authorization requests are timing out, investigate the latency of the external authorization service. Consider increasing timeout values or optimizing the service for faster response times.
  3. Missing Permissions: Verify that the user or service account has the required permissions to access the protected resources. Review the authorization policies and ensure they are correctly defined.
  4. Incorrect Policy Configuration: Validate that the authorization policies are correctly formatted and applied. Misconfigured policies can lead to unexpected behavior or access denials.
  5. Service Availability: Confirm that the external authorization service is up and running. Use monitoring tools to check for service outages or high latency.
Issue Potential Cause Solution
Authorization Denied Incorrect headers or tokens Verify client credentials and configuration
Timeouts Slow external authorization service Increase timeout values or optimize service performance
Missing Permissions Insufficient user/service permissions Review and update authorization policies
Policy Misconfiguration Incorrectly formatted or applied policies Validate and correct policy definitions
Service Outage External authorization service down Check service status and restart if necessary
Note: Use logging and monitoring tools to track authorization requests and responses for better visibility into issues.

Key Troubleshooting Steps

  • Verify client credentials and headers
  • Check external authorization service availability
  • Review policy configurations for correctness
  • Monitor response times and timeouts
  • Use logs to identify root causes of failures

11. Integrating OPA with Service Mesh

Example: OPA Integration Configuration

authorization:
  opa:
    enabled: true
    policyPath: /policies/authz.rego
    bundle:
      name: authz-bundle
      url: http://opa-service:8181/bundles/authz
    config:
      service: opa-service
      port: 8181
Configuration Description Default Value Notes
enabled Enables OPA authorization false Set to true to enable OPA integration
policyPath Path to OPA policy file /policies/authz.rego Must be accessible to the service mesh
bundle.name Name of OPA bundle authz-bundle Used for fetching policy bundles
bundle.url URL to OPA bundle endpoint http://opa-service:8181/bundles/authz Must be reachable from the service mesh
config.service OPA service name opa-service Used for internal communication
config.port OPA service port 8181 Port where OPA listens for requests
Note: OPA integration requires the service mesh to support external authorization and has proper network access to the OPA service.
Warning: Ensure that policy bundles are properly validated before deployment to avoid authorization failures.

Key Considerations

  • OPA must be configured to handle authorization requests from the service mesh
  • Policies should be versioned and managed through a secure bundle system
  • Network policies must allow communication between the service mesh and OPA
  • OPA should be monitored for performance and authorization decision latency

12. Managing External Authorization Performance

Aspect Description Impact
Authorization Latency Time taken to process authorization requests Can significantly affect API response times if not optimized
Caching Strategy Use of in-memory or distributed caches (e.g., Redis, Memcached) Reduces repeated authorization checks; improves throughput
Rate Limiting Controlled number of authorization requests per second Prevents system overload; maintains service stability
Batching Requests Processing multiple authorization checks in one go Reduces network overhead and improves efficiency
Async Processing Non-blocking authorization checks using async/await or queues Improves responsiveness for concurrent requests

Example: Caching Authorization Results

const cache = new Map();
async function authorizeRequest(request) {
  const key = 'auth_' + request.user.id + '_' + request.resource;
  if (cache.has(key)) {
    return cache.get(key);
  }
  const result = await externalAuthzService.check(request);
  cache.set(key, result);
  return result;
}
Note: Caching should be used carefully to avoid stale permissions. Implement TTLs or invalidation strategies.
Warning: High authorization latency can cause cascading failures in microservices. Monitor and optimize regularly.

Performance Optimization Tips

  • Implement efficient caching with TTLs
  • Use rate limiting to prevent abuse
  • Batch authorization checks where possible
  • Use async processing for non-critical flows
  • Monitor authorization latency and set alerts

Was this article helpful?

Related Cheat Sheets