How do I expose internal APIs to partners safely?

To expose internal APIs to partners safely, treat it as a controlled product boundary, not a direct hole into your internal network.

Core principles

1. Never expose internal services directly

   • Put an API gateway / reverse proxy in front.
   • Keep internal APIs on private networks.
   • Create a partner-facing facade with only the endpoints and fields they need.

2. Use strong partner authentication and authorization

   • Prefer OAuth 2.0 / OpenID Connect for partner identity.
   • Use mTLS for service-to-service or high-trust B2B integrations.
   • Issue per-partner credentials and scopes.
   • Enforce least privilege: each partner gets only the endpoints, data, and actions they require.

3. Segment and isolate

   • Separate partner APIs from internal APIs by:
     • network segment
     • DNS name
     • gateway route
     • IAM policy
   • Consider a dedicated integration environment or tenant isolation for sensitive partners.

4. Minimize the data surface

   • Return only necessary fields.
   • Avoid exposing internal IDs, debug fields, stack traces, or raw backend objects.
   • Use DTOs / response mapping instead of passing internal schemas through.

5. Validate everything

   • Strict schema validation for requests and responses.
   • Enforce size limits, rate limits, and allowed values.
   • Reject unknown fields if possible.
   • Sanitize logs and payloads to avoid secrets leakage.

6. Protect against abuse

   • Rate limiting / quotas per partner.
   • Burst controls and circuit breakers.
   • WAF rules if internet-facing.
   • Replay protection and request signing where appropriate.
   • Monitoring for unusual traffic or access patterns.

7. Control data exposure

   • Classify data: public, partner-shareable, confidential, regulated.
   • Apply field-level authorization and data masking.
   • Avoid exposing PII unless contractually and legally required.
   • Support data retention, deletion, and audit requirements.

8. Audit and observe

   • Log partner identity, endpoint, request ID, and outcome.
   • Keep audit trails for sensitive operations.
   • Centralize metrics, traces, and alerts for anomalies.
   • Make logs tamper-resistant if compliance matters.

9. Version and change safely

   • Version partner APIs explicitly.
   • Use backward-compatible changes whenever possible.
   • Publish deprecation timelines.
   • Maintain contract tests so internal changes don’t break partners.

10. Test like an attacker

• Run threat modeling on the partner boundary.
• Test auth bypass, IDOR, injection, rate limit evasion, and privilege escalation.
• Verify that internal endpoints are not reachable via alternate paths.

A secure reference architecture

• Partner → CDN/WAF → API Gateway
• Gateway handles:
  • authn/authz
  • rate limits
  • request validation
  • logging
  • routing
• Gateway forwards only to:
  • partner API service or
  • adapter layer that maps to internal services
• Internal services remain private and protected by service identity and network controls

Practical checklist

• Dedicated partner API domain
• API gateway in front
• OAuth2/OIDC or mTLS
• Per-partner scopes and quotas
• Response filtering / DTO mapping
• Network isolation from internal APIs
• Audit logs and anomaly detection
• Versioning and deprecation policy
• Contract and security testing

If you want, I can also give you:

• a reference architecture diagram
• a cloud-specific setup for AWS/Azure/GCP
• a partner API security checklist
• or a sample policy model for scopes, quotas, and field-level access.