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:

1 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)

1 POST /a2a
2 Authorization: Bearer <oauth-access-token>
3 Content-Type: application/json
4 
5 {
6   "jsonrpc": "2.0",
7   "method": "tasks/send",
8   "params": { "..." }
9 }

IDA-Enhanced (DID Auth + IBCT)

1 POST /a2a
2 Authorization: DIDAuth <did-auth-token>
3 X-IDA-IBCT: <ibct-token>
4 X-IDA-Agent-DID: did:adi:agent:buyer01...
5 Content-Type: application/json
6 
7 {
8   "jsonrpc": "2.0",
9   "method": "tasks/send",
10   "params": {
11     "id": "task-001",
12     "message": {
13       "role": "user",
14       "parts": [
15         {
16           "type": "text",
17           "text": "Compare prices for organic milk across all authorized merchants"
18         }
19       ]
20     }
21   },
22 
23   "ida": {
24     "agentDid": "did:adi:agent:buyer01...",
25     "ibct": "eyJhbGciOiJFZERTQSJ9...",
26     "delegationChain": ["urn:uuid:root-delegation"]
27   }
28 }

Task Send with IDA Identity

Request

1 {
2   "jsonrpc": "2.0",
3   "method": "tasks/send",
4   "params": {
5     "id": "task-price-compare-001",
6     "message": {
7       "role": "user",
8       "parts": [
9         {
10           "type": "text",
11           "text": "Find the best price for 1 gallon organic milk"
12         }
13       ]
14     },
15     "metadata": {
16       "ida_agent_did": "did:adi:agent:buyer01...",
17       "ida_ibct": "eyJhbGciOiJFZERTQSJ9...",
18       "ida_required_trust_score": 70
19     }
20   },
21   "id": "req-001"
22 }

Response (Working)

1 {
2   "jsonrpc": "2.0",
3   "result": {
4     "id": "task-price-compare-001",
5     "status": {
6       "state": "working",
7       "message": "Comparing prices across 2 merchants..."
8     },
9     "metadata": {
10       "ida_server_agent_did": "did:adi:agent:seller01...",
11       "ida_audit_receipt_id": "receipt-abc123"
12     }
13   },
14   "id": "req-001"
15 }

Response (Done)

1 {
2   "jsonrpc": "2.0",
3   "result": {
4     "id": "task-price-compare-001",
5     "status": {
6       "state": "done"
7     },
8     "artifacts": [
9       {
10         "name": "price-comparison",
11         "parts": [
12           {
13             "type": "text",
14             "text": "Best price: FreshMart - $5.99/gallon (OrganicCo: $6.49)"
15           }
16         ]
17       }
18     ],
19     "metadata": {
20       "ida_audit_receipt": {
21         "id": "receipt-abc123",
22         "agentDid": "did:adi:agent:seller01...",
23         "result": "success",
24         "signature": "z58DAdFfa9SkqZMVPxAQpic7..."
25       }
26     }
27   },
28   "id": "req-001"
29 }

Server Agent Setup

Express.js A2A Server with IDA

1 import express from 'express';
2 import { IDAClient } from '@ida/sdk';
3 
4 const app = express();
5 const ida = new IDAClient({ apiUrl: 'http://localhost:8080' });
6 
7 // Serve Agent Card
8 app.get('/.well-known/agent.json', (req, res) => {
9   res.json({
10     name: "Price Comparison Agent",
11     description: "Compares prices across merchants",
12     url: "https://price-agent.example.com",
13     identity: {
14       did: "did:adi:agent:seller01...",
15       operatorDid: "did:adi:merchant001...",
16       trustScore: 88
17     },
18     skills: [
19       {
20         id: "price-compare",
21         name: "Price Comparison",
22         tags: ["prices", "comparison"]
23       }
24     ],
25     authentication: {
26       schemes: [
27         { scheme: "did-auth", didMethod: "did:adi" },
28         { scheme: "oauth2", flows: ["client_credentials"] }
29       ]
30     }
31   });
32 });
33 
34 // A2A endpoint
35 app.post('/a2a', async (req, res) => {
36   const { method, params, ida: idaParams } = req.body;
37 
38   // Verify client agent's identity
39   if (idaParams?.ibct) {
40     const verification = await ida.verifyIBCT(idaParams.ibct);
41     if (!verification.valid) {
42       return res.json({
43         jsonrpc: "2.0",
44         error: { code: -32001, message: "IBCT verification failed" }
45       });
46     }
47   }
48 
49   if (method === 'tasks/send') {
50     // Process task
51     const result = await handleTask(params);
52     return res.json({
53       jsonrpc: "2.0",
54       result: { id: params.id, status: { state: "done" }, artifacts: [result] }
55     });
56   }
57 });

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.