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>

src/controllers/DelegationController.ts

@@ -0,0 +1,177 @@
+/**
+ * Delegation Controller for SentryAgent.ai AgentIdP.
+ * HTTP handlers for A2A delegation endpoints. No business logic — delegates to DelegationService.
+ */
+
+import { Request, Response, NextFunction } from 'express';
+import { DelegationService } from '../services/DelegationService.js';
+import { AuthorizationError, ValidationError } from '../utils/errors.js';
+import {
+  delegationsCreatedTotal,
+  delegationsVerifiedTotal,
+  delegationsRevokedTotal,
+} from '../metrics/registry.js';
+
+/**
+ * Controller for A2A delegation endpoints.
+ * Receives DelegationService via constructor injection.
+ */
+export class DelegationController {
+  /**
+   * @param delegationService - The A2A delegation service.
+   */
+  constructor(private readonly delegationService: DelegationService) {}
+
+  /**
+   * Handles POST /oauth2/token/delegate — creates a delegation chain.
+   *
+   * @param req - Express request with CreateDelegationRequest body.
+   * @param res - Express response.
+   * @param next - Express next function.
+   */
+  createDelegation = async (req: Request, res: Response, next: NextFunction): Promise<void> => {
+    try {
+      if (!req.user) {
+        throw new AuthorizationError();
+      }
+
+      const { delegateeAgentId, scopes, ttlSeconds } = req.body as {
+        delegateeAgentId?: unknown;
+        scopes?: unknown;
+        ttlSeconds?: unknown;
+      };
+
+      if (typeof delegateeAgentId !== 'string' || !delegateeAgentId) {
+        throw new ValidationError('delegateeAgentId is required and must be a string.');
+      }
+      if (!Array.isArray(scopes) || scopes.length === 0) {
+        throw new ValidationError('scopes must be a non-empty array.');
+      }
+      if (typeof ttlSeconds !== 'number' || !Number.isInteger(ttlSeconds)) {
+        throw new ValidationError('ttlSeconds must be an integer.');
+      }
+
+      const tenantId = req.user.organization_id ?? 'org_system';
+      const delegatorAgentId = req.user.sub;
+      const delegatorScopes = req.user.scope ? req.user.scope.split(' ') : [];
+      const ipAddress = req.ip ?? '0.0.0.0';
+      const userAgent = req.headers['user-agent'] ?? 'unknown';
+
+      const chain = await this.delegationService.createDelegation(
+        tenantId,
+        delegatorAgentId,
+        delegatorScopes,
+        { delegateeAgentId, scopes: scopes as string[], ttlSeconds },
+        ipAddress,
+        userAgent,
+      );
+
+      delegationsCreatedTotal.labels(tenantId).inc();
+
+      res.status(201).json({
+        delegationToken: chain.delegationToken,
+        chainId: chain.id,
+        delegatorAgentId: chain.delegatorAgentId,
+        delegateeAgentId: chain.delegateeAgentId,
+        scopes: chain.scopes,
+        expiresAt: chain.expiresAt.toISOString(),
+      });
+    } catch (err) {
+      next(err);
+    }
+  };
+
+  /**
+   * Handles POST /oauth2/token/verify-delegation — verifies a delegation token.
+   *
+   * @param req - Express request with delegationToken body.
+   * @param res - Express response.
+   * @param next - Express next function.
+   */
+  verifyDelegation = async (req: Request, res: Response, next: NextFunction): Promise<void> => {
+    try {
+      if (!req.user) {
+        throw new AuthorizationError();
+      }
+
+      const { delegationToken } = req.body as { delegationToken?: unknown };
+
+      if (typeof delegationToken !== 'string' || !delegationToken) {
+        throw new ValidationError('delegationToken is required and must be a string.');
+      }
+
+      const agentId = req.user.sub;
+      const tenantId = req.user.organization_id ?? 'org_system';
+      const ipAddress = req.ip ?? '0.0.0.0';
+      const userAgent = req.headers['user-agent'] ?? 'unknown';
+
+      const result = await this.delegationService.verifyDelegation(
+        delegationToken,
+        agentId,
+        ipAddress,
+        userAgent,
+      );
+
+      const outcomeLabel = result.valid
+        ? 'valid'
+        : result.revokedAt !== null
+          ? 'revoked'
+          : new Date() > result.expiresAt
+            ? 'expired'
+            : 'invalid';
+
+      delegationsVerifiedTotal.labels(tenantId, outcomeLabel).inc();
+
+      res.status(200).json({
+        valid: result.valid,
+        chainId: result.chainId,
+        delegatorAgentId: result.delegatorAgentId,
+        delegateeAgentId: result.delegateeAgentId,
+        scopes: result.scopes,
+        issuedAt: result.issuedAt.toISOString(),
+        expiresAt: result.expiresAt.toISOString(),
+        revokedAt: result.revokedAt ? result.revokedAt.toISOString() : null,
+      });
+    } catch (err) {
+      next(err);
+    }
+  };
+
+  /**
+   * Handles DELETE /oauth2/token/delegate/:chainId — revokes a delegation chain.
+   *
+   * @param req - Express request with chainId path param.
+   * @param res - Express response.
+   * @param next - Express next function.
+   */
+  revokeDelegation = async (req: Request, res: Response, next: NextFunction): Promise<void> => {
+    try {
+      if (!req.user) {
+        throw new AuthorizationError();
+      }
+
+      const { chainId } = req.params;
+      if (!chainId) {
+        throw new ValidationError('chainId path parameter is required.');
+      }
+
+      const requestingAgentId = req.user.sub;
+      const tenantId = req.user.organization_id ?? 'org_system';
+      const ipAddress = req.ip ?? '0.0.0.0';
+      const userAgent = req.headers['user-agent'] ?? 'unknown';
+
+      await this.delegationService.revokeDelegation(
+        chainId,
+        requestingAgentId,
+        ipAddress,
+        userAgent,
+      );
+
+      delegationsRevokedTotal.labels(tenantId).inc();
+
+      res.status(204).send();
+    } catch (err) {
+      next(err);
+    }
+  };
+}

src/db/migrations/024_add_delegation_chains.sql

@@ -0,0 +1,30 @@
+-- Migration 024: Add delegation_chains table for A2A authorization (Phase 5 WS2)
+-- Creates the delegation_chains table that stores A2A delegation tokens and their
+-- verification signatures, enabling agent-to-agent authority delegation.
+
+CREATE TABLE delegation_chains (
+    id                  UUID        PRIMARY KEY DEFAULT gen_random_uuid(),
+    tenant_id           VARCHAR(40) NOT NULL,
+    delegator_agent_id  UUID        NOT NULL REFERENCES agents(agent_id) ON DELETE CASCADE,
+    delegatee_agent_id  UUID        NOT NULL REFERENCES agents(agent_id) ON DELETE CASCADE,
+    scopes              TEXT[]      NOT NULL,
+    delegation_token    TEXT        NOT NULL UNIQUE,
+    signature           TEXT        NOT NULL,
+    ttl_seconds         INTEGER     NOT NULL CHECK (ttl_seconds BETWEEN 60 AND 86400),
+    issued_at           TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    expires_at          TIMESTAMPTZ NOT NULL,
+    revoked_at          TIMESTAMPTZ,
+    created_at          TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- Index for token lookup (verify-delegation hot path)
+CREATE UNIQUE INDEX idx_delegation_chains_token ON delegation_chains(delegation_token);
+
+-- Index for listing delegations by delegator agent
+CREATE INDEX idx_delegation_chains_delegator ON delegation_chains(delegator_agent_id, tenant_id);
+
+-- Index for listing delegations by delegatee agent
+CREATE INDEX idx_delegation_chains_delegatee ON delegation_chains(delegatee_agent_id, tenant_id);
+
+-- Index for cleanup of expired chains
+CREATE INDEX idx_delegation_chains_expires_at ON delegation_chains(expires_at);

src/routes/delegation.ts

@@ -0,0 +1,52 @@
+/**
+ * A2A Delegation routes for SentryAgent.ai AgentIdP.
+ * All three delegation endpoints require Bearer token authentication.
+ */
+
+import { Router, RequestHandler } from 'express';
+import { DelegationController } from '../controllers/DelegationController.js';
+import { asyncHandler } from '../utils/asyncHandler.js';
+
+/**
+ * Creates and returns the Express router for A2A delegation endpoints.
+ *
+ * Routes:
+ *   POST   /oauth2/token/delegate              — create a delegation chain
+ *   POST   /oauth2/token/verify-delegation     — verify a delegation token
+ *   DELETE /oauth2/token/delegate/:chainId     — revoke a delegation chain
+ *
+ * All routes are protected by the JWT authentication middleware.
+ *
+ * @param controller - The delegation controller instance.
+ * @param authMiddleware - The JWT authentication middleware.
+ * @returns Configured Express router.
+ */
+export function createDelegationRouter(
+  controller: DelegationController,
+  authMiddleware: RequestHandler,
+): Router {
+  const router = Router();
+
+  // POST /oauth2/token/delegate — authenticated; creates a delegation chain
+  router.post(
+    '/oauth2/token/delegate',
+    authMiddleware,
+    asyncHandler(controller.createDelegation.bind(controller)),
+  );
+
+  // POST /oauth2/token/verify-delegation — authenticated; verifies a delegation token
+  router.post(
+    '/oauth2/token/verify-delegation',
+    authMiddleware,
+    asyncHandler(controller.verifyDelegation.bind(controller)),
+  );
+
+  // DELETE /oauth2/token/delegate/:chainId — authenticated; revokes a delegation chain
+  router.delete(
+    '/oauth2/token/delegate/:chainId',
+    authMiddleware,
+    asyncHandler(controller.revokeDelegation.bind(controller)),
+  );
+
+  return router;
+}

src/services/DelegationService.ts

@@ -0,0 +1,334 @@
+/**
+ * A2A Delegation Service for SentryAgent.ai AgentIdP.
+ * Business logic for creating, verifying, and revoking delegation chains.
+ */
+
+import { Pool, QueryResult } from 'pg';
+import { AuditService } from './AuditService.js';
+import {
+  DelegationChain,
+  CreateDelegationRequest,
+  DelegationVerificationResult,
+  DelegationTokenPayload,
+} from '../types/delegation.js';
+import {
+  signDelegationPayload,
+  verifyDelegationSignature,
+  generateDelegationToken,
+} from '../utils/delegationCrypto.js';
+import {
+  AgentNotFoundError,
+  ValidationError,
+  AuthorizationError,
+  CredentialAlreadyRevokedError,
+} from '../utils/errors.js';
+
+/** Database row shape returned by delegation_chains queries. */
+interface DelegationChainRow {
+  id: string;
+  tenant_id: string;
+  delegator_agent_id: string;
+  delegatee_agent_id: string;
+  scopes: string[];
+  delegation_token: string;
+  signature: string;
+  ttl_seconds: number;
+  issued_at: Date;
+  expires_at: Date;
+  revoked_at: Date | null;
+  created_at: Date;
+}
+
+/** Interface contract for the delegation service. */
+export interface IDelegationService {
+  /**
+   * Create a delegation chain from delegator to delegatee.
+   * Validates scope subset, signs payload, inserts DB row, writes audit log.
+   */
+  createDelegation(
+    tenantId: string,
+    delegatorAgentId: string,
+    delegatorScopes: string[],
+    request: CreateDelegationRequest,
+    ipAddress: string,
+    userAgent: string,
+  ): Promise<DelegationChain>;
+
+  /**
+   * Verify a delegation token. Returns chain details with valid flag.
+   * Does not throw on expired/revoked — returns valid: false.
+   */
+  verifyDelegation(
+    delegationToken: string,
+    agentId: string,
+    ipAddress: string,
+    userAgent: string,
+  ): Promise<DelegationVerificationResult>;
+
+  /**
+   * Revoke a delegation chain. Only the delegator may revoke.
+   */
+  revokeDelegation(
+    chainId: string,
+    requestingAgentId: string,
+    ipAddress: string,
+    userAgent: string,
+  ): Promise<void>;
+}
+
+/**
+ * Implementation of IDelegationService.
+ * Uses PostgreSQL for persistence and HMAC-SHA256 for delegation payload signing.
+ */
+export class DelegationService implements IDelegationService {
+  private readonly delegationSecret: string;
+
+  /**
+   * @param pool - PostgreSQL connection pool.
+   * @param auditService - Audit log service for recording delegation events.
+   */
+  constructor(
+    private readonly pool: Pool,
+    private readonly auditService: AuditService,
+  ) {
+    this.delegationSecret =
+      process.env['DELEGATION_SECRET'] ?? process.env['JWT_SECRET'] ?? 'delegation-secret-change-me';
+  }
+
+  /**
+   * Creates a delegation chain, signing the payload and storing it in the database.
+   *
+   * @param tenantId - The organization ID of the delegating agent.
+   * @param delegatorAgentId - UUID of the agent granting delegation.
+   * @param delegatorScopes - Scopes held by the delegator (from their JWT).
+   * @param request - Delegation request body.
+   * @param ipAddress - Caller IP for audit log.
+   * @param userAgent - Caller user-agent for audit log.
+   * @returns The created DelegationChain record.
+   * @throws ValidationError on invalid scopes, ttl, or self-delegation.
+   * @throws AgentNotFoundError if delegateeAgentId does not exist in the same tenant.
+   */
+  async createDelegation(
+    tenantId: string,
+    delegatorAgentId: string,
+    delegatorScopes: string[],
+    request: CreateDelegationRequest,
+    ipAddress: string,
+    userAgent: string,
+  ): Promise<DelegationChain> {
+    const { delegateeAgentId, scopes, ttlSeconds } = request;
+
+    // Validate ttl range
+    if (ttlSeconds < 60 || ttlSeconds > 86400) {
+      throw new ValidationError('ttlSeconds must be between 60 and 86400.', { code: 'INVALID_TTL' });
+    }
+
+    // Reject self-delegation
+    if (delegateeAgentId === delegatorAgentId) {
+      throw new ValidationError('An agent cannot delegate to itself.', { code: 'SELF_DELEGATION' });
+    }
+
+    // Validate scopes are a strict subset of the delegator's own scopes
+    const disallowedScopes = scopes.filter((s) => !delegatorScopes.includes(s));
+    if (disallowedScopes.length > 0) {
+      throw new ValidationError(
+        `Requested scopes exceed delegator permissions: ${disallowedScopes.join(', ')}`,
+        { code: 'INVALID_SCOPES', disallowedScopes },
+      );
+    }
+
+    // Verify delegatee exists in the same tenant
+    const delegateeResult: QueryResult<{ agent_id: string }> = await this.pool.query(
+      `SELECT agent_id FROM agents WHERE agent_id = $1 AND organization_id = $2 AND status = 'active'`,
+      [delegateeAgentId, tenantId],
+    );
+    if (delegateeResult.rows.length === 0) {
+      throw new AgentNotFoundError(delegateeAgentId);
+    }
+
+    const now = new Date();
+    const expiresAt = new Date(now.getTime() + ttlSeconds * 1000);
+    const chainId = generateDelegationToken(); // UUID for the chain id
+    const delegationToken = generateDelegationToken(); // UUID for the token value
+
+    const payload: DelegationTokenPayload = {
+      chainId,
+      tenantId,
+      delegatorAgentId,
+      delegateeAgentId,
+      scopes,
+      issuedAt: now.toISOString(),
+      expiresAt: expiresAt.toISOString(),
+    };
+
+    const signature = signDelegationPayload(payload, this.delegationSecret);
+
+    const insertResult: QueryResult<DelegationChainRow> = await this.pool.query(
+      `INSERT INTO delegation_chains
+         (id, tenant_id, delegator_agent_id, delegatee_agent_id, scopes,
+          delegation_token, signature, ttl_seconds, issued_at, expires_at)
+       VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10)
+       RETURNING *`,
+      [
+        chainId,
+        tenantId,
+        delegatorAgentId,
+        delegateeAgentId,
+        scopes,
+        delegationToken,
+        signature,
+        ttlSeconds,
+        now,
+        expiresAt,
+      ],
+    );
+
+    await this.auditService.logEvent(
+      delegatorAgentId,
+      'delegation.created',
+      'success',
+      ipAddress,
+      userAgent,
+      { chainId, delegateeAgentId, scopes, ttlSeconds },
+      tenantId,
+    );
+
+    return this.rowToChain(insertResult.rows[0]);
+  }
+
+  /**
+   * Verifies a delegation token. Returns valid: false for expired or revoked chains
+   * rather than throwing an error.
+   *
+   * @param delegationToken - The delegation token to verify.
+   * @param agentId - The agent performing verification (for audit log).
+   * @param ipAddress - Caller IP for audit log.
+   * @param userAgent - Caller user-agent for audit log.
+   * @returns DelegationVerificationResult with valid flag.
+   * @throws AgentNotFoundError if no chain is found for the given token.
+   */
+  async verifyDelegation(
+    delegationToken: string,
+    agentId: string,
+    ipAddress: string,
+    userAgent: string,
+  ): Promise<DelegationVerificationResult> {
+    const result: QueryResult<DelegationChainRow> = await this.pool.query(
+      `SELECT * FROM delegation_chains WHERE delegation_token = $1`,
+      [delegationToken],
+    );
+
+    if (result.rows.length === 0) {
+      throw new AgentNotFoundError(delegationToken);
+    }
+
+    const row = result.rows[0];
+    const now = new Date();
+
+    const payload: DelegationTokenPayload = {
+      chainId: row.id,
+      tenantId: row.tenant_id,
+      delegatorAgentId: row.delegator_agent_id,
+      delegateeAgentId: row.delegatee_agent_id,
+      scopes: row.scopes,
+      issuedAt: row.issued_at.toISOString(),
+      expiresAt: row.expires_at.toISOString(),
+    };
+
+    const signatureValid = verifyDelegationSignature(payload, row.signature, this.delegationSecret);
+    const notExpired = row.expires_at > now;
+    const notRevoked = row.revoked_at === null;
+    const valid = signatureValid && notExpired && notRevoked;
+
+    await this.auditService.logEvent(
+      agentId,
+      'delegation.verified',
+      'success',
+      ipAddress,
+      userAgent,
+      { chainId: row.id, valid, signatureValid, notExpired, notRevoked },
+      row.tenant_id,
+    );
+
+    return {
+      valid,
+      chainId: row.id,
+      delegatorAgentId: row.delegator_agent_id,
+      delegateeAgentId: row.delegatee_agent_id,
+      scopes: row.scopes,
+      issuedAt: row.issued_at,
+      expiresAt: row.expires_at,
+      revokedAt: row.revoked_at,
+    };
+  }
+
+  /**
+   * Revokes a delegation chain. Only the original delegator may revoke.
+   *
+   * @param chainId - UUID of the delegation chain to revoke.
+   * @param requestingAgentId - The agent attempting revocation (must be the delegator).
+   * @param ipAddress - Caller IP for audit log.
+   * @param userAgent - Caller user-agent for audit log.
+   * @throws AgentNotFoundError if no chain with this ID exists.
+   * @throws AuthorizationError if the requesting agent is not the delegator.
+   * @throws CredentialAlreadyRevokedError if the chain is already revoked.
+   */
+  async revokeDelegation(
+    chainId: string,
+    requestingAgentId: string,
+    ipAddress: string,
+    userAgent: string,
+  ): Promise<void> {
+    const result: QueryResult<DelegationChainRow> = await this.pool.query(
+      `SELECT * FROM delegation_chains WHERE id = $1`,
+      [chainId],
+    );
+
+    if (result.rows.length === 0) {
+      throw new AgentNotFoundError(chainId);
+    }
+
+    const row = result.rows[0];
+
+    if (row.delegator_agent_id !== requestingAgentId) {
+      throw new AuthorizationError('Only the delegating agent may revoke this delegation chain.');
+    }
+
+    if (row.revoked_at !== null) {
+      throw new CredentialAlreadyRevokedError(chainId, row.revoked_at.toISOString());
+    }
+
+    await this.pool.query(
+      `UPDATE delegation_chains SET revoked_at = NOW() WHERE id = $1`,
+      [chainId],
+    );
+
+    await this.auditService.logEvent(
+      requestingAgentId,
+      'delegation.revoked',
+      'success',
+      ipAddress,
+      userAgent,
+      { chainId, delegateeAgentId: row.delegatee_agent_id },
+      row.tenant_id,
+    );
+  }
+
+  /** Maps a database row to a DelegationChain domain object. */
+  private rowToChain(row: DelegationChainRow): DelegationChain {
+    return {
+      id: row.id,
+      tenantId: row.tenant_id,
+      delegatorAgentId: row.delegator_agent_id,
+      delegateeAgentId: row.delegatee_agent_id,
+      scopes: row.scopes,
+      delegationToken: row.delegation_token,
+      signature: row.signature,
+      ttlSeconds: row.ttl_seconds,
+      issuedAt: row.issued_at,
+      expiresAt: row.expires_at,
+      revokedAt: row.revoked_at,
+      createdAt: row.created_at,
+    };
+  }
+}

src/types/delegation.ts

@@ -0,0 +1,53 @@
+/**
+ * TypeScript interfaces for the A2A (Agent-to-Agent) delegation subsystem.
+ * All delegation types are defined here — no inline type definitions in services or controllers.
+ */
+
+/** A delegation chain record as stored in the database. */
+export interface DelegationChain {
+  id: string;
+  tenantId: string;
+  delegatorAgentId: string;
+  delegateeAgentId: string;
+  scopes: string[];
+  delegationToken: string;
+  signature: string;
+  ttlSeconds: number;
+  issuedAt: Date;
+  expiresAt: Date;
+  revokedAt: Date | null;
+  createdAt: Date;
+}
+
+/** Request body for creating a new delegation. */
+export interface CreateDelegationRequest {
+  /** UUID of the agent receiving delegated authority. Must be in the same tenant. */
+  delegateeAgentId: string;
+  /** Scopes to delegate. Must be a strict subset of the delegator's own scopes. */
+  scopes: string[];
+  /** Delegation lifetime in seconds. Min: 60, Max: 86400. */
+  ttlSeconds: number;
+}
+
+/** Result of verifying a delegation token. Never throws on expired/revoked — returns valid: false. */
+export interface DelegationVerificationResult {
+  valid: boolean;
+  chainId: string;
+  delegatorAgentId: string;
+  delegateeAgentId: string;
+  scopes: string[];
+  issuedAt: Date;
+  expiresAt: Date;
+  revokedAt: Date | null;
+}
+
+/** Payload signed by HMAC-SHA256 to produce the delegation signature. */
+export interface DelegationTokenPayload {
+  chainId: string;
+  tenantId: string;
+  delegatorAgentId: string;
+  delegateeAgentId: string;
+  scopes: string[];
+  issuedAt: string; // ISO 8601
+  expiresAt: string; // ISO 8601
+}

src/utils/delegationCrypto.ts

@@ -0,0 +1,45 @@
+/**
+ * Cryptographic utilities for A2A delegation chain signing and verification.
+ * Uses HMAC-SHA256 to produce and verify delegation payload signatures.
+ */
+
+import { createHmac, randomUUID } from 'crypto';
+import { DelegationTokenPayload } from '../types/delegation.js';
+
+/**
+ * Signs a delegation payload using HMAC-SHA256.
+ *
+ * @param payload - The delegation token payload to sign.
+ * @param secret - The HMAC signing secret.
+ * @returns Hex-encoded HMAC-SHA256 digest of the serialised payload.
+ */
+export function signDelegationPayload(payload: DelegationTokenPayload, secret: string): string {
+  const data = JSON.stringify(payload);
+  return createHmac('sha256', secret).update(data).digest('hex');
+}
+
+/**
+ * Verifies a delegation payload against an expected HMAC-SHA256 signature.
+ *
+ * @param payload - The delegation token payload to verify.
+ * @param signature - The hex-encoded signature to check against.
+ * @param secret - The HMAC signing secret.
+ * @returns `true` if the signature is valid, `false` otherwise.
+ */
+export function verifyDelegationSignature(
+  payload: DelegationTokenPayload,
+  signature: string,
+  secret: string,
+): boolean {
+  const expected = signDelegationPayload(payload, secret);
+  return expected === signature;
+}
+
+/**
+ * Generates a unique delegation token (UUID v4).
+ *
+ * @returns A random UUID string to use as the delegation token.
+ */
+export function generateDelegationToken(): string {
+  return randomUUID();
+}