API Gateway

The gateway centralizes identity enforcement by validating credentials at the perimeter before any request reaches a backend service. It acts as a Policy Enforcement Point (PEP) , translating external tokens into internal workload identities.

• Integrates with OAuth 2.0 and OpenID Connect (OIDC) flows
• Performs JWT Validation on every request, checking signature, expiry, and claims
• Enforces Attribute-Based Access Control (ABAC) by evaluating user, device, and location context
• Converts external user identities into SPIFFE-compatible workload identities for service-to-service calls

A critical defensive mechanism that protects backend services from abuse, accidental overload, and denial-of-service attacks by controlling request velocity.

• Applies token bucket and sliding window algorithms to enforce per-client quotas
• Returns 429 Too Many Requests with Retry-After headers to well-behaved clients
• Differentiates limits by user tier, API endpoint, or originating IP
• Prevents cascading failures by shedding excess load before it reaches fragile downstream systems

The gateway decouples the client-facing API contract from the internal service topology, enabling backend evolution without breaking consumers.

• Routes requests based on URL path, HTTP method, headers, or query parameters
• Performs content-based routing, directing calls to different service versions based on payload fields
• Implements API composition, aggregating data from multiple microservices into a single client response
• Supports canary deployments and blue-green releases by shifting traffic percentages between service versions

The gateway serves as the cryptographic boundary, handling the computationally expensive TLS handshake from external clients and establishing new secure channels to internal services.

• Terminates public-facing TLS 1.3 connections with hardware-accelerated encryption
• Initiates Mutual TLS (mTLS) to backend services, presenting the gateway's own X.509 certificate
• Enforces Forward Secrecy cipher suites to protect past sessions against future key compromise
• Bridges untrusted external networks to the zero-trust internal mesh without exposing backend certificates

As the single ingress point, the gateway generates the golden signals—latency, traffic, errors, and saturation—for every API interaction without requiring instrumentation of backend code.

• Emits structured access logs including request path, status code, latency, and authenticated principal
• Exports OpenTelemetry traces with span context propagated to downstream services via headers
• Exposes Prometheus metrics endpoints for request rates, error percentages, and latency percentiles
• Provides real-time dashboards for east-west traffic control visibility at the ingress boundary

The gateway manages the coexistence of multiple API versions, enabling graceful deprecation and backward compatibility without fragmenting the client ecosystem.

• Routes requests to the correct backend based on version identifiers in URL paths, headers, or accept parameters
• Injects deprecation warnings via Sunset and Deprecation HTTP headers on older endpoints
• Supports request/response transformation to adapt between breaking schema changes across versions
• Enforces API retirement schedules by blocking traffic to sunsetted endpoints after a communicated deadline

The API gateway functions as the quintessential Policy Enforcement Point in a zero-trust architecture. It is the network component that intercepts every API call and enforces the access decision dictated by the Policy Decision Point (PDP). The gateway activates the specific rule—whether it's blocking an unauthenticated request, injecting an authorization header, or terminating a connection that fails mTLS validation. Without a PEP like an API gateway, authorization policies remain abstract definitions with no physical execution mechanism in the data path.

A cryptographic protocol where the API gateway and the connecting client both present and validate X.509 certificates during the TLS handshake. Unlike standard TLS, which only authenticates the server, mTLS provides bidirectional identity verification for service-to-service communication. In a zero-trust AI network, the gateway uses mTLS to cryptographically confirm that a model inference request originates from a verified workload, not an impostor. This eliminates reliance on network-level identifiers like IP addresses, which can be spoofed, and binds every API call to a verifiable SPIFFE-compliant workload identity.

A dedicated infrastructure layer that externalizes service-to-service communication logic from application code, often using a sidecar proxy pattern. While an API gateway manages north-south traffic (external clients to internal services), a service mesh handles east-west traffic (service-to-service within the cluster). In modern deployments, the gateway and mesh converge—an API gateway can integrate with a mesh like Istio or Linkerd to route requests directly to mesh-internal endpoints, leveraging the mesh's mTLS identity and traffic policies. This unified control plane ensures consistent observability and security across all traffic flows.

The process by which an API gateway verifies the integrity, authenticity, and claims of a JSON Web Token presented in the Authorization: Bearer header. The gateway performs cryptographic signature verification using the identity provider's public key (typically obtained via a JWKS endpoint), then validates standard claims:

• iss (issuer): Must match the trusted authorization server
• aud (audience): Must include this specific API
• exp (expiration): Token must not be expired
• nbf (not before): Token must be currently valid Failed validation results in an immediate HTTP 401 Unauthorized response, offloading authentication logic from backend services.

A cloud-based proxy that controls access to applications based on the verified identity and context of the user, effectively replacing a traditional VPN for application-level access. An IAP extends the API gateway pattern by integrating deeply with an identity provider's OIDC flows and evaluating rich contextual signals—device posture, geolocation, and risk score—before granting access. When combined with an API gateway, the IAP handles user authentication at the edge, while the gateway enforces fine-grained authorization and rate limiting for specific API endpoints, creating a defense-in-depth architecture.