Federator Service as a REST API Gateway

[nikan-negaresh-informed]

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Summary: Federator service as a REST API Gateway

Type: Story
Component: Federator
Labels: federation, api-gateway, routing, m2m

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Description

The Federator must be extended to act as a REST API Gateway, providing a unified entry point for inter-organisational data exchange requests across the federation. Rather than point-to-point connections between nodes, consuming nodes route outbound requests through the Federator, which handles mTLS termination, request authentication, routing to the correct target node, and response relay. This centralises cross-cutting concerns (security, redaction, audit) at the gateway layer.

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Acceptance Criteria

• Federator accepts inbound REST requests from local services and routes them to the correct target node based on a configurable routing table
• All outbound connections to target nodes are established over mTLS using the node's role-scoped certificates
• Inbound requests are authenticated before routing — unauthenticated requests are rejected with 401
• Routing table maps request path or destination identifier to target node endpoint; configuration is externally managed and hot-reloadable
• Federator relays the target node's response back to the caller, preserving HTTP status codes
• Requests and responses pass through the redaction pipeline prior to relay
• Each routed request produces an audit log entry: source, destination node identity, path, timestamp, and status
• Target node unavailability returns a structured error to the caller — Federator does not hang indefinitely (configurable timeout)

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Technical Notes

• Spring Boot with Spring Cloud Gateway or a lightweight WebClient-based proxy is suitable; evaluate Spring Cloud Gateway for built-in filter chain support (aligns with redaction and audit interceptor pattern)
• mTLS outbound connections must use role-scoped producer/consumer certificates from the shared volume (aligns with multi-cert story)
• Routing table: file-backed or Management Node-sourced; externalise as federator.gateway.routes; hot-reload via WatchService consistent with cert reload pattern
• Request timeout: federator.gateway.timeout-ms, default recommended 30s
• Redaction pipeline (from data redaction story) must be inserted as a gateway filter on the outbound path

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Out of Scope

• Rate limiting and throttling (subsequent story)
• Service discovery (routing table is statically configured in this iteration)
• Human operator traffic

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Dependencies

• Role-scoped producer/consumer certificates available on shared volume
• Data redaction pipeline implemented and filter-insertable
• Target nodes expose REST endpoints compatible with gateway relay

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Definition of Done

• Request routed end-to-end over mTLS and response relayed correctly
• Unauthenticated request rejection verified
• Routing table hot-reload confirmed without restart
• Redaction pipeline applied on gateway path verified
• Timeout and unavailability behaviour confirmed
• PR reviewed and merged