@absolutejs/agent-exchange-a2a

Interoperable A2A client and server adapters for Agent Exchange. The adapter discovers an A2A 1.0 Agent Card, requires the Agent Exchange extension to be advertised, activates it through A2A-Extensions, and places only the core package's opaque safe reference in task history. Dedicated cards can require the extension; shared cards can advertise it as optional.

The server authenticates the caller through the host-supplied A2A authorization function, then passes that verified caller and opaque reference to a deterministic executor. The executor must resolve the full request from trusted server state, verify the OAuth delegation and any signed standing mandate, and authorize it before source access. Results are projected into a bounded redacted receipt.

import {
  connectAgentExchangeA2a,
  createAgentExchangeA2aHandler,
} from "@absolutejs/agent-exchange-a2a";

Prepared exchanges

A recipient that needs the complete request before the opaque A2A signal can advertise a same-origin preparation endpoint in the extension parameters:

const handler = createAgentExchangeA2aHandler({
  agentCard,
  authorize,
  execute,
  preparationEndpoint: "https://recipient.example/agent-exchange/requests",
  taskStore,
});

connectAgentExchangeA2a() discovers that endpoint. Each send(request) posts the complete request there and verifies that the response contains the exact derived opaque reference before sending anything on A2A. Preparation and A2A credentials remain separate:

const client = await connectAgentExchangeA2a({
  headers: () => a2aAuthorizationHeaders(),
  origin: "https://recipient.example",
  preparationHeaders: () => preparationAuthorizationHeaders(),
});

const receipt = await client.send(request);

The preparation endpoint uses application/vnd.absolutejs.agent-exchange-preparation+json, accepts { request }, and returns { reference }. It must authenticate the delegated caller, validate and durably protect the request, reject replay, and return Cache-Control: no-store. The adapter rejects cross-origin preparation URLs, redirects, response media-type substitution, extra response fields, and any reference that differs from the request.

Hosts with an existing trusted preparation channel can instead supply a prepare(request, context) callback. Omitting both an advertised endpoint and a callback retains out-of-band preparation mode.

The adapter intentionally does not transmit signed mandates, OAuth tokens, mailbox credentials, encrypted envelopes, account references, or verification codes through A2A. See the extension specification.

This is an experimental 0.x package and has not been independently audited.