A2A Protocol Support | IDA — Identity for the AI Age

IDA integrates with Google’s Agent-to-Agent (A2A) protocol to enable cross-vendor agent collaboration with verifiable identity. A2A defines how agents discover each other, negotiate tasks, and exchange results.

A2A Protocol Overview

Agent Card Serving

IDA agents serve A2A-compatible Agent Cards at the .well-known endpoint:

GET https://agent.example.com/.well-known/agent.json

See Agent Discovery & Cards for the full Agent Card format.

Task Lifecycle

A2A defines a task lifecycle that IDA extends with identity verification:

State	Description	IDA Extension
`submitted`	Task received by server agent	IBCT verified, delegation checked
`working`	Agent is processing the task	Audit trail started
`input-required`	Agent needs more information	HITL if high-risk
`done`	Task completed successfully	Audit receipt signed
`failed`	Task failed	Failure logged to audit trail
`canceled`	Task canceled by client	Cancellation logged

Authentication Flow

IDA extends A2A authentication with DID-based auth:

Standard A2A (OAuth 2.0)

POST /a2a
Authorization: Bearer <oauth-access-token>
Content-Type: application/json
{
  "jsonrpc": "2.0",
  "method": "tasks/send",
  "params": { "..." }
}

IDA-Enhanced (DID Auth + IBCT)

POST /a2a
Authorization: DIDAuth <did-auth-token>
X-IDA-IBCT: <ibct-token>
X-IDA-Agent-DID: did:adi:agent:buyer01...
Content-Type: application/json
{
  "jsonrpc": "2.0",
  "method": "tasks/send",
  "params": {
    "id": "task-001",
    "message": {
      "role": "user",
      "parts": [
        {
          "type": "text",
          "text": "Compare prices for organic milk across all authorized merchants"
        }
      ]
    }
  },
  "ida": {
    "agentDid": "did:adi:agent:buyer01...",
    "ibct": "eyJhbGciOiJFZERTQSJ9...",
    "delegationChain": ["urn:uuid:root-delegation"]
  }
}

Task Send with IDA Identity

Request

{
  "jsonrpc": "2.0",
  "method": "tasks/send",
  "params": {
    "id": "task-price-compare-001",
    "message": {
      "role": "user",
      "parts": [
        {
          "type": "text",
          "text": "Find the best price for 1 gallon organic milk"
        }
      ]
    },
    "metadata": {
      "ida_agent_did": "did:adi:agent:buyer01...",
      "ida_ibct": "eyJhbGciOiJFZERTQSJ9...",
      "ida_required_trust_score": 70
    }
  },
  "id": "req-001"
}

Response (Working)

{
  "jsonrpc": "2.0",
  "result": {
    "id": "task-price-compare-001",
    "status": {
      "state": "working",
      "message": "Comparing prices across 2 merchants..."
    },
    "metadata": {
      "ida_server_agent_did": "did:adi:agent:seller01...",
      "ida_audit_receipt_id": "receipt-abc123"
    }
  },
  "id": "req-001"
}

Response (Done)

{
  "jsonrpc": "2.0",
  "result": {
    "id": "task-price-compare-001",
    "status": {
      "state": "done"
    },
    "artifacts": [
      {
        "name": "price-comparison",
        "parts": [
          {
            "type": "text",
            "text": "Best price: FreshMart - $5.99/gallon (OrganicCo: $6.49)"
          }
        ]
      }
    ],
    "metadata": {
      "ida_audit_receipt": {
        "id": "receipt-abc123",
        "agentDid": "did:adi:agent:seller01...",
        "result": "success",
        "signature": "z58DAdFfa9SkqZMVPxAQpic7..."
      }
    }
  },
  "id": "req-001"
}

Server Agent Setup

Express.js A2A Server with IDA

import express from 'express';
import { IDAClient } from '@ida/sdk';
const app = express();
const ida = new IDAClient({ apiUrl: 'http://localhost:8080' });
// Serve Agent Card
app.get('/.well-known/agent.json', (req, res) => {
  res.json({
    name: "Price Comparison Agent",
    description: "Compares prices across merchants",
    url: "https://price-agent.example.com",
    identity: {
      did: "did:adi:agent:seller01...",
      operatorDid: "did:adi:merchant001...",
      trustScore: 88
    },
    skills: [
      {
        id: "price-compare",
        name: "Price Comparison",
        tags: ["prices", "comparison"]
      }
    ],
    authentication: {
      schemes: [
        { scheme: "did-auth", didMethod: "did:adi" },
        { scheme: "oauth2", flows: ["client_credentials"] }
      ]
    }
  });
});
// A2A endpoint
app.post('/a2a', async (req, res) => {
  const { method, params, ida: idaParams } = req.body;
  // Verify client agent's identity
  if (idaParams?.ibct) {
    const verification = await ida.verifyIBCT(idaParams.ibct);
    if (!verification.valid) {
      return res.json({
        jsonrpc: "2.0",
        error: { code: -32001, message: "IBCT verification failed" }
      });
    }
  }
  if (method === 'tasks/send') {
    // Process task
    const result = await handleTask(params);
    return res.json({
      jsonrpc: "2.0",
      result: { id: params.id, status: { state: "done" }, artifacts: [result] }
    });
  }
});

Multi-Agent Collaboration

A2A enables multi-agent workflows where IDA provides the trust layer:

Each A2A interaction carries:

The sending agent’s IBCT (proving delegation)
The task payload
Audit receipts for every step

A2A + DID Auth vs OAuth 2.0

Feature	OAuth 2.0	DID Auth + IBCT
Identity proof	Client ID + secret	Cryptographic DID signature
Delegation	Not supported	Full delegation chain
Scope enforcement	OAuth scopes (static)	IBCT scope (per-invocation)
Trust scoring	Not available	On-chain trust score
Audit trail	Application-level	Cryptographic receipts
Revocation	Token revocation	Real-time delegation revocation

IDA supports both authentication methods. OAuth 2.0 is available for backward compatibility with non-IDA agents.