feat(phase-5): WS2 — A2A Authorization

Implements agent-to-agent delegation chains:
- Migration 024: delegation_chains table with HMAC signature, TTL, revocation
- DelegationCrypto: HMAC-SHA256 sign/verify, UUID token generation
- DelegationService: create (scope subset validation, self-delegation guard,
  same-tenant delegatee check), verify (returns valid: false on expired/revoked,
  never throws), revoke (delegator-only, conflict guard)
- DelegationController + router at /oauth2/token/delegate (POST/DELETE) and
  /oauth2/token/verify-delegation (POST)
- Feature-flagged behind A2A_ENABLED env var (default on)
- Prometheus metrics: delegations_created/verified/revoked_total
- 33 tests (unit + integration): all pass, DelegationService 87.5%+ branch coverage

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/unit/utils/delegationCrypto.test.ts

@@ -0,0 +1,89 @@
+/**
+ * Unit tests for src/utils/delegationCrypto.ts
+ */
+
+import {
+  signDelegationPayload,
+  verifyDelegationSignature,
+  generateDelegationToken,
+} from '../../../src/utils/delegationCrypto';
+import { DelegationTokenPayload } from '../../../src/types/delegation';
+
+const MOCK_PAYLOAD: DelegationTokenPayload = {
+  chainId: 'chain-uuid-1234',
+  tenantId: 'org_system',
+  delegatorAgentId: 'delegator-uuid',
+  delegateeAgentId: 'delegatee-uuid',
+  scopes: ['agents:read', 'tokens:read'],
+  issuedAt: '2026-04-03T00:00:00.000Z',
+  expiresAt: '2026-04-03T01:00:00.000Z',
+};
+
+const SECRET = 'test-hmac-secret';
+
+describe('delegationCrypto', () => {
+  describe('signDelegationPayload', () => {
+    it('returns a non-empty hex string', () => {
+      const sig = signDelegationPayload(MOCK_PAYLOAD, SECRET);
+      expect(typeof sig).toBe('string');
+      expect(sig.length).toBeGreaterThan(0);
+      // SHA-256 hex = 64 chars
+      expect(sig).toMatch(/^[0-9a-f]{64}$/);
+    });
+
+    it('produces the same signature for the same payload and secret', () => {
+      const sig1 = signDelegationPayload(MOCK_PAYLOAD, SECRET);
+      const sig2 = signDelegationPayload(MOCK_PAYLOAD, SECRET);
+      expect(sig1).toBe(sig2);
+    });
+
+    it('produces different signatures for different secrets', () => {
+      const sig1 = signDelegationPayload(MOCK_PAYLOAD, 'secret-a');
+      const sig2 = signDelegationPayload(MOCK_PAYLOAD, 'secret-b');
+      expect(sig1).not.toBe(sig2);
+    });
+
+    it('produces different signatures for different payloads', () => {
+      const payload2 = { ...MOCK_PAYLOAD, chainId: 'different-chain-uuid' };
+      const sig1 = signDelegationPayload(MOCK_PAYLOAD, SECRET);
+      const sig2 = signDelegationPayload(payload2, SECRET);
+      expect(sig1).not.toBe(sig2);
+    });
+  });
+
+  describe('verifyDelegationSignature', () => {
+    it('returns true for a valid sign/verify round-trip', () => {
+      const signature = signDelegationPayload(MOCK_PAYLOAD, SECRET);
+      expect(verifyDelegationSignature(MOCK_PAYLOAD, signature, SECRET)).toBe(true);
+    });
+
+    it('returns false when the payload has been tampered with', () => {
+      const signature = signDelegationPayload(MOCK_PAYLOAD, SECRET);
+      const tampered = { ...MOCK_PAYLOAD, scopes: ['admin:orgs'] };
+      expect(verifyDelegationSignature(tampered, signature, SECRET)).toBe(false);
+    });
+
+    it('returns false when the secret does not match', () => {
+      const signature = signDelegationPayload(MOCK_PAYLOAD, SECRET);
+      expect(verifyDelegationSignature(MOCK_PAYLOAD, signature, 'wrong-secret')).toBe(false);
+    });
+
+    it('returns false for an empty signature string', () => {
+      expect(verifyDelegationSignature(MOCK_PAYLOAD, '', SECRET)).toBe(false);
+    });
+  });
+
+  describe('generateDelegationToken', () => {
+    it('returns a UUID v4 string', () => {
+      const token = generateDelegationToken();
+      expect(token).toMatch(
+        /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i,
+      );
+    });
+
+    it('generates unique tokens on each call', () => {
+      const tokens = new Set(Array.from({ length: 50 }, () => generateDelegationToken()));
+      expect(tokens.size).toBe(50);
+    });
+  });
+});