feat: add agw impl [EXPERIMENTAL]

[Schmarvinius]

feat: Add SAP Agent Gateway Adapter with IAS JWT-Bearer Token Exchange

This PR introduces a new n8n-to-gateway adapter that routes n8n workflow invocations through the SAP Agent Gateway, implementing the first authentication gate: IAS JWT-bearer token exchange via mTLS.

🆕 New Files

lib/auth/agent-gateway-credentials.js
Resolves Agent Gateway credentials from cds.requires.n8n.credentials.agentGateway. Supports flexible configuration via:

• Inline values
• File references (certificateFile, privateKeyFile) for local development
• A single crdFile JSON (consumed resource definition)

Validates required fields (clientid, iasUrl, certificate, key) and normalizes the IAS URL to its origin for @sap/xssec discovery.

lib/auth/token-exchange.js
Performs the IAS JWT-bearer assertion ("Exchange Access Token") using @sap/xssec's IdentityService. Exchanges the authenticated user's JWT for a token scoped to the Agent Gateway via urn:sap:identity:application:provider:name:agent-gateway. Includes a lazily-initialized, keyed cache for the IdentityService instance and exposes test hooks (_resetCache, _setIdentityServiceFactory).

srv/n8n-to-gateway.js + srv/n8n-to-gateway.cds
The new gateway adapter extending N8nRestService. Implements Gate 1 (IAS assertion) fully. Gate 2+ (actual Agent Gateway invocation via MCP endpoint) is stubbed with a TODO and a warning log.

🔧 Modified Files

lib/handlers/triggerHandler.js

• Switches from n8n.trigger(...) to n8n.send({ event: 'trigger', ... }) to support outbox-persisted headers.
• Captures the user's JWT synchronously in the originating request context and forwards it via x-agw-user-assertion header for async delivery.

package.json

• Adds @sap/xssec: ^4 as a runtime dependency.
• Registers the new n8n-to-gateway kind in the CDS plugin configuration.

Change Type

🆕 New Feature

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