Overview
Access Gateways provide a centralized enforcement point for authentication, authorization, and security policies, acting as a reverse proxy between users and backend applications. They eliminate the need for each application to implement its own authentication logic, creating a consistent security perimeter. A well-architected gateway reduces integration complexity, provides a single point for policy enforcement, and enables legacy applications to participate in modern SSO without code changes. Organizations without centralized access gateways typically suffer from inconsistent security policies, duplicated authentication code, and difficulty enforcing organization-wide access controls.
Architecture & Reference Patterns
Pattern 1: Centralized Reverse Proxy Gateway
A single gateway cluster handles all inbound traffic, authenticates users against the IdP, and forwards authenticated requests to backend applications with identity headers. Best for organizations with moderate traffic and centralized infrastructure. The gateway terminates TLS, validates sessions, enforces authorization policies, and injects identity headers (X-Forwarded-User, X-Forwarded-Groups) before proxying to backends.
Pattern 2: Distributed Sidecar Proxy (Service Mesh)
Each microservice has a co-located proxy (sidecar) that handles mTLS, authentication, and authorization. Control plane distributes policies centrally while enforcement happens at the edge of each service. Ideal for Kubernetes-native environments with service-to-service communication requirements. Products like Istio, Linkerd, and Consul Connect implement this pattern.
Pattern 3: API Gateway with Identity-Aware Routing
Specialized for API traffic, this pattern combines rate limiting, request transformation, and OAuth token validation. The gateway validates access tokens, extracts claims, and routes to appropriate backends based on scopes and resource paths. Kong, AWS API Gateway, and Apigee follow this model.
Pattern 4: Cloud-Native Application Load Balancer
Cloud providers offer identity-aware load balancers (AWS ALB with OIDC, GCP IAP) that integrate directly with IdPs. Simpler to operate but less flexible than dedicated gateway products. Best for cloud-native applications that can accept cloud provider lock-in.
Key Decisions
| Decision | Options | Recommendation | Notes / Gotchas |
|---|---|---|---|
| Gateway placement | DMZ, internal network, cloud edge | Cloud edge or DMZ for external apps, internal for service mesh | Internal gateways reduce latency but require careful network segmentation |
| Session handling | Gateway-managed sessions, pass-through tokens, token exchange | Gateway-managed for web apps, pass-through for APIs | Gateway sessions require sticky sessions or distributed session store |
| Identity header format | Custom headers, JWT injection, SAML assertion | JWT in Authorization header for new apps | Legacy apps may expect specific header formats—document and standardize |
| High availability model | Active-active, active-passive, global load balancing | Active-active with health checks | Session affinity complicates active-active; use distributed session store |
| TLS termination | At gateway, at backend, both (re-encryption) | Terminate at gateway, re-encrypt to backend | End-to-end TLS adds latency but may be required for compliance |
| Legacy app integration | Header injection, agent-based, form-fill | Header injection with X-Forwarded headers | Form-fill is fragile and should be avoided if possible |
Implementation Approach
Phase 0: Discovery
Inputs: Application inventory, current authentication methods, network topology diagrams, traffic patterns and volumes, compliance requirements Outputs: Application categorization by authentication capability (SAML, OIDC, headers-only, none), traffic analysis report, candidate applications for gateway protection, risk assessment of current state
Phase 1: Design
Inputs: Discovery outputs, IdP capabilities and constraints, security requirements, SLA requirements Outputs: Target-state architecture diagram, gateway product selection rationale, header injection specification, session management design, high availability design, capacity planning document
Phase 2: Build & Integrate
Inputs: Design documents, gateway licenses/subscriptions, test applications, IdP configuration access Outputs: Gateway infrastructure deployed, IdP-to-gateway integration complete, pilot application integrated and tested, monitoring and alerting configured, runbooks drafted
Phase 3: Rollout
Inputs: Tested gateway infrastructure, prioritized application list, change management approvals, rollback procedures Outputs: Applications migrated in waves, user communication completed, helpdesk trained, performance baselines established, incident response procedures validated
Phase 4: Operate
Inputs: Production gateway environment, monitoring dashboards, operational procedures Outputs: SLA metrics reported, security incidents investigated, capacity adjusted as needed, new application onboarding streamlined, continuous improvement backlog maintained
Deliverables
- Target-state architecture diagram showing gateway placement, traffic flows, and IdP integration
- Gateway configuration standards document (header formats, timeout settings, security policies)
- Application integration guide with step-by-step onboarding instructions
- Decision log capturing key architectural choices and rationale
- Implementation backlog with prioritized epics and stories
- Runbooks for common operations (certificate rotation, session troubleshooting, emergency bypass)
- Capacity planning model with growth projections
Risks & Failure Modes
| Risk | Likelihood | Impact | Early Signals | Mitigation |
|---|---|---|---|---|
| Gateway becomes single point of failure | M | H | Availability metrics degrading, near-miss incidents | Deploy active-active across zones, implement health-based routing, maintain emergency bypass |
| Performance degradation under load | M | H | Latency percentiles increasing, queue depth growing | Load test before production, implement auto-scaling, set up performance alerts |
| Session store failure causes mass logout | L | H | Session validation errors, user complaints spike | Use distributed session store with replication, implement graceful degradation |
| Certificate expiration causes outage | M | H | Certificate monitoring alerts | Automate certificate renewal, implement 30/7/1 day alerts, use short-lived certificates |
| Backend header injection bypass | L | H | Security audit findings | Block direct backend access at network level, validate source IP at backend |
| Incompatible application breaks after migration | M | M | Testing failures, user-reported issues | Comprehensive testing in staging, maintain rollback capability, canary deployments |
KPIs / Outcomes
- Gateway availability: Target 99.95% uptime
- Authentication latency: P95 under 200ms for cached sessions, under 500ms for new authentications
- Application onboarding time: Reduce from weeks to days (target: 5 business days for standard apps)
- Security incidents from authentication bypass: Zero tolerance
- Percentage of applications behind gateway: Track progress toward 100% coverage
- Help desk tickets related to access issues: Should decrease after initial rollout