feat(federation): Step-CA client service for grant certs (FED-M2-04) (#494)

apps/gateway/src/app.module.ts

@@ -24,6 +24,7 @@ import { GCModule } from './gc/gc.module.js';
 import { ReloadModule } from './reload/reload.module.js';
 import { WorkspaceModule } from './workspace/workspace.module.js';
 import { QueueModule } from './queue/queue.module.js';
+import { FederationModule } from './federation/federation.module.js';
 import { ThrottlerGuard, ThrottlerModule } from '@nestjs/throttler';
 
 @Module({
@@ -52,6 +53,7 @@ import { ThrottlerGuard, ThrottlerModule } from '@nestjs/throttler';
     QueueModule,
     ReloadModule,
     WorkspaceModule,
+    FederationModule,
   ],
   controllers: [HealthController],
   providers: [

apps/gateway/src/federation/ca.dto.ts

@@ -0,0 +1,57 @@
+/**
+ * DTOs for the Step-CA client service (FED-M2-04).
+ *
+ * IssueCertRequestDto  — input to CaService.issueCert()
+ * IssuedCertDto        — output from CaService.issueCert()
+ */
+
+import { IsInt, IsNotEmpty, IsOptional, IsString, IsUUID, Max, Min } from 'class-validator';
+
+export class IssueCertRequestDto {
+  /**
+   * PEM-encoded PKCS#10 Certificate Signing Request.
+   * The CSR must already include the desired SANs.
+   */
+  @IsString()
+  @IsNotEmpty()
+  csrPem!: string;
+
+  /**
+   * UUID of the federation_grants row this certificate is being issued for.
+   * Embedded as the `mosaic_grant_id` custom OID extension.
+   */
+  @IsUUID()
+  grantId!: string;
+
+  /**
+   * UUID of the local user on whose behalf the cert is being issued.
+   * Embedded as the `mosaic_subject_user_id` custom OID extension.
+   */
+  @IsUUID()
+  subjectUserId!: string;
+
+  /**
+   * Requested certificate validity in seconds.
+   * Hard cap: 900 s (15 minutes). Default: 300 s (5 minutes).
+   * The service will always clamp to 900 s regardless of this value.
+   */
+  @IsOptional()
+  @IsInt()
+  @Min(60)
+  @Max(15 * 60)
+  ttlSeconds: number = 300;
+}
+
+export class IssuedCertDto {
+  /** PEM-encoded leaf certificate returned by step-ca. */
+  certPem!: string;
+
+  /**
+   * PEM-encoded full certificate chain (leaf + intermediates + root).
+   * Falls back to `certPem` when step-ca returns no `certChain` field.
+   */
+  certChainPem!: string;
+
+  /** Decimal serial number string of the issued certificate. */
+  serialNumber!: string;
+}

apps/gateway/src/federation/ca.service.spec.ts

@@ -0,0 +1,577 @@
+/**
+ * Unit tests for CaService — Step-CA client (FED-M2-04).
+ *
+ * Coverage:
+ *  - Happy path: returns IssuedCertDto with certPem, certChainPem, serialNumber
+ *  - certChainPem fallback: falls back to certPem when certChain absent
+ *  - certChainPem from ca field: uses crt+ca when certChain absent but ca present
+ *  - HTTP 401: throws CaServiceError with cause + remediation
+ *  - HTTP non-401 error: throws CaServiceError
+ *  - Malformed CSR: throws before HTTP call (INVALID_CSR)
+ *  - Non-JSON response: throws CaServiceError
+ *  - HTTPS connection error: throws CaServiceError
+ *  - JWT custom claims: mosaic_grant_id and mosaic_subject_user_id present in OTT payload
+ *    verified with jose.jwtVerify (real signature check)
+ *  - CaServiceError: has cause + remediation properties
+ *  - Missing crt in response: throws CaServiceError
+ *  - Real CSR validation: valid P-256 CSR passes; malformed CSR fails with INVALID_CSR
+ *  - provisionerPassword never appears in CaServiceError messages
+ *  - HTTPS-only enforcement: http:// URL throws in constructor
+ */
+
+import 'reflect-metadata';
+import { describe, it, expect, vi, beforeEach, type Mock } from 'vitest';
+import { jwtVerify, exportJWK, generateKeyPair } from 'jose';
+import { Pkcs10CertificateRequestGenerator } from '@peculiar/x509';
+
+// ---------------------------------------------------------------------------
+// Mock node:https BEFORE importing CaService so the mock is in place when
+// the module is loaded. Vitest/ESM require vi.mock at the top level.
+// ---------------------------------------------------------------------------
+
+vi.mock('node:https', () => {
+  const mockRequest = vi.fn();
+  const mockAgent = vi.fn().mockImplementation(() => ({}));
+  return {
+    default: { request: mockRequest, Agent: mockAgent },
+    request: mockRequest,
+    Agent: mockAgent,
+  };
+});
+
+vi.mock('node:fs', () => {
+  const mockReadFileSync = vi
+    .fn()
+    .mockReturnValue('-----BEGIN CERTIFICATE-----\nFAKEROOT\n-----END CERTIFICATE-----\n');
+  return {
+    default: { readFileSync: mockReadFileSync },
+    readFileSync: mockReadFileSync,
+  };
+});
+
+// ---------------------------------------------------------------------------
+// Helpers
+// ---------------------------------------------------------------------------
+
+// Real self-signed EC P-256 certificate generated with openssl for testing.
+// openssl req -x509 -newkey ec -pkeyopt ec_paramgen_curve:P-256 -nodes -keyout /dev/null \
+//   -out /dev/stdout -subj "/CN=test" -days 1
+const FAKE_CERT_PEM = `-----BEGIN CERTIFICATE-----
+MIIBdDCCARmgAwIBAgIUM+iUJSayN+PwXkyVN6qwSY7sr6gwCgYIKoZIzj0EAwIw
+DzENMAsGA1UEAwwEdGVzdDAeFw0yNjA0MjIwMzE5MTlaFw0yNjA0MjMwMzE5MTla
+MA8xDTALBgNVBAMMBHRlc3QwWTATBgcqhkjOPQIBBggqhkjOPQMBBwNCAAR21kHL
+n1GmFQ4TEBw3EA53pD+2McIBf5WcoHE+x0eMz5DpRKJe0ksHwOVN5Yev5d57kb+4
+MvG1LhbHCB/uQo8So1MwUTAdBgNVHQ4EFgQUPq0pdIGiQ7pLBRXICS8GTliCrLsw
+HwYDVR0jBBgwFoAUPq0pdIGiQ7pLBRXICS8GTliCrLswDwYDVR0TAQH/BAUwAwEB
+/zAKBggqhkjOPQQDAgNJADBGAiEAypJqyC6S77aQ3eEXokM6sgAsD7Oa3tJbCbVm
+zG3uJb0CIQC1w+GE+Ad0OTR5Quja46R1RjOo8ydpzZ7Fh4rouAiwEw==
+-----END CERTIFICATE-----
+`;
+
+// Use a second copy of the same cert for the CA field in tests.
+const FAKE_CA_PEM = FAKE_CERT_PEM;
+
+const GRANT_ID = 'a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11';
+const SUBJECT_USER_ID = 'b1ffcd00-0d1c-5f09-cc7e-7cc0ce491b22';
+
+// ---------------------------------------------------------------------------
+// Generate a real EC P-256 key pair and CSR for integration-style tests
+// ---------------------------------------------------------------------------
+
+// We generate this once at module level so it's available to all tests.
+// The key pair and CSR PEM are populated asynchronously in the test that needs them.
+
+let realCsrPem: string;
+
+async function generateRealCsr(): Promise<string> {
+  const { privateKey, publicKey } = await generateKeyPair('ES256');
+  // Export public key JWK for potential verification (not used here but confirms key is exportable)
+  await exportJWK(publicKey);
+
+  // Use @peculiar/x509 to build a proper CSR
+  const csr = await Pkcs10CertificateRequestGenerator.create({
+    name: 'CN=test.federation.local',
+    signingAlgorithm: { name: 'ECDSA', hash: 'SHA-256' },
+    keys: { privateKey, publicKey },
+  });
+
+  return csr.toString('pem');
+}
+
+// ---------------------------------------------------------------------------
+// Setup env before importing service
+// We use an EC P-256 key pair here so the JWK-based signing works.
+// The key pair is generated once and stored in module-level vars.
+// ---------------------------------------------------------------------------
+
+// Real EC P-256 test JWK (test-only, never used in production).
+// Generated with node webcrypto for use in unit tests.
+const TEST_EC_PRIVATE_JWK = {
+  key_ops: ['sign'],
+  ext: true,
+  kty: 'EC',
+  x: 'Xq2RjZctcPcUMU14qfjs3MtZTmFk8z1lFGQyypgXZOU',
+  y: 't8w9Cbt4RVmR47Wnb_i5cLwefEnMcvwse049zu9Rl_E',
+  crv: 'P-256',
+  d: 'TM6N79w1HE-PiML5Td4mbXfJaLHEaZrVyVrrwlJv7q8',
+  kid: 'test-ec-kid',
+};
+
+const TEST_EC_PUBLIC_JWK = {
+  key_ops: ['verify'],
+  ext: true,
+  kty: 'EC',
+  x: 'Xq2RjZctcPcUMU14qfjs3MtZTmFk8z1lFGQyypgXZOU',
+  y: 't8w9Cbt4RVmR47Wnb_i5cLwefEnMcvwse049zu9Rl_E',
+  crv: 'P-256',
+  kid: 'test-ec-kid',
+};
+
+process.env['STEP_CA_URL'] = 'https://step-ca:9000';
+process.env['STEP_CA_PROVISIONER_KEY_JSON'] = JSON.stringify(TEST_EC_PRIVATE_JWK);
+process.env['STEP_CA_ROOT_CERT_PATH'] = '/fake/root.pem';
+
+// Import AFTER env is set and mocks are registered
+import * as httpsModule from 'node:https';
+import { CaService, CaServiceError } from './ca.service.js';
+import type { IssueCertRequestDto } from './ca.dto.js';
+
+// ---------------------------------------------------------------------------
+// Helper to build a mock https.request that simulates step-ca
+// ---------------------------------------------------------------------------
+
+function makeHttpsMock(statusCode: number, body: unknown, errorMsg?: string): void {
+  const mockReq = {
+    write: vi.fn(),
+    end: vi.fn(),
+    on: vi.fn(),
+    setTimeout: vi.fn(),
+  };
+
+  (httpsModule.request as unknown as Mock).mockImplementation(
+    (
+      _options: unknown,
+      callback: (res: {
+        statusCode: number;
+        on: (event: string, cb: (chunk?: Buffer) => void) => void;
+      }) => void,
+    ) => {
+      const mockRes = {
+        statusCode,
+        on: (event: string, cb: (chunk?: Buffer) => void) => {
+          if (event === 'data') {
+            if (body !== undefined) {
+              cb(Buffer.from(typeof body === 'string' ? body : JSON.stringify(body)));
+            }
+          }
+          if (event === 'end') {
+            cb();
+          }
+        },
+      };
+
+      if (errorMsg) {
+        // Simulate a connection error via the req.on('error') handler
+        mockReq.on.mockImplementation((event: string, cb: (err: Error) => void) => {
+          if (event === 'error') {
+            setImmediate(() => cb(new Error(errorMsg)));
+          }
+        });
+      } else {
+        // Normal flow: call the response callback
+        setImmediate(() => callback(mockRes));
+      }
+
+      return mockReq;
+    },
+  );
+}
+
+// ---------------------------------------------------------------------------
+// Tests
+// ---------------------------------------------------------------------------
+
+describe('CaService', () => {
+  let service: CaService;
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+    service = new CaService();
+  });
+
+  function makeReq(overrides: Partial<IssueCertRequestDto> = {}): IssueCertRequestDto {
+    // Use a real CSR if available; fall back to a minimal placeholder
+    const defaultCsr = realCsrPem ?? makeFakeCsr();
+    return {
+      csrPem: defaultCsr,
+      grantId: GRANT_ID,
+      subjectUserId: SUBJECT_USER_ID,
+      ttlSeconds: 300,
+      ...overrides,
+    };
+  }
+
+  function makeFakeCsr(): string {
+    // A structurally valid-looking CSR header/footer (body will fail crypto verify)
+    return `-----BEGIN CERTIFICATE REQUEST-----\nMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA0000000000000000AAAA\n-----END CERTIFICATE REQUEST-----\n`;
+  }
+
+  // -------------------------------------------------------------------------
+  // Real CSR generation — runs once and populates realCsrPem
+  // -------------------------------------------------------------------------
+
+  it('generates a real P-256 CSR that passes validateCsr', async () => {
+    realCsrPem = await generateRealCsr();
+    expect(realCsrPem).toMatch(/BEGIN CERTIFICATE REQUEST/);
+
+    // Now test that the service's validateCsr accepts it.
+    // We call it indirectly via issueCert with a successful mock.
+    makeHttpsMock(200, { crt: FAKE_CERT_PEM, certChain: [FAKE_CERT_PEM, FAKE_CA_PEM] });
+    const result = await service.issueCert(makeReq({ csrPem: realCsrPem }));
+    expect(result.certPem).toBe(FAKE_CERT_PEM);
+  });
+
+  it('throws INVALID_CSR for a malformed PEM-shaped CSR', async () => {
+    const malformedCsr =
+      '-----BEGIN CERTIFICATE REQUEST-----\nTm90QVJlYWxDU1I=\n-----END CERTIFICATE REQUEST-----\n';
+
+    await expect(service.issueCert(makeReq({ csrPem: malformedCsr }))).rejects.toSatisfy(
+      (err: unknown) => {
+        if (!(err instanceof CaServiceError)) return false;
+        expect(err.code).toBe('INVALID_CSR');
+        return true;
+      },
+    );
+  });
+
+  // -------------------------------------------------------------------------
+  // Happy path
+  // -------------------------------------------------------------------------
+
+  it('returns IssuedCertDto on success (certChain present)', async () => {
+    if (!realCsrPem) realCsrPem = await generateRealCsr();
+    makeHttpsMock(200, {
+      crt: FAKE_CERT_PEM,
+      certChain: [FAKE_CERT_PEM, FAKE_CA_PEM],
+    });
+
+    const result = await service.issueCert(makeReq());
+
+    expect(result.certPem).toBe(FAKE_CERT_PEM);
+    expect(result.certChainPem).toContain(FAKE_CERT_PEM);
+    expect(result.certChainPem).toContain(FAKE_CA_PEM);
+    expect(typeof result.serialNumber).toBe('string');
+  });
+
+  // -------------------------------------------------------------------------
+  // certChainPem fallback — certChain absent, ca field present
+  // -------------------------------------------------------------------------
+
+  it('builds certChainPem from crt+ca when certChain is absent', async () => {
+    if (!realCsrPem) realCsrPem = await generateRealCsr();
+    makeHttpsMock(200, {
+      crt: FAKE_CERT_PEM,
+      ca: FAKE_CA_PEM,
+    });
+
+    const result = await service.issueCert(makeReq());
+
+    expect(result.certPem).toBe(FAKE_CERT_PEM);
+    expect(result.certChainPem).toContain(FAKE_CERT_PEM);
+    expect(result.certChainPem).toContain(FAKE_CA_PEM);
+  });
+
+  // -------------------------------------------------------------------------
+  // certChainPem fallback — no certChain, no ca field
+  // -------------------------------------------------------------------------
+
+  it('falls back to certPem alone when certChain and ca are absent', async () => {
+    if (!realCsrPem) realCsrPem = await generateRealCsr();
+    makeHttpsMock(200, { crt: FAKE_CERT_PEM });
+
+    const result = await service.issueCert(makeReq());
+
+    expect(result.certPem).toBe(FAKE_CERT_PEM);
+    expect(result.certChainPem).toBe(FAKE_CERT_PEM);
+  });
+
+  // -------------------------------------------------------------------------
+  // HTTP 401
+  // -------------------------------------------------------------------------
+
+  it('throws CaServiceError on HTTP 401', async () => {
+    if (!realCsrPem) realCsrPem = await generateRealCsr();
+    makeHttpsMock(401, { message: 'Unauthorized' });
+
+    await expect(service.issueCert(makeReq())).rejects.toSatisfy((err: unknown) => {
+      if (!(err instanceof CaServiceError)) return false;
+      expect(err.message).toMatch(/401/);
+      expect(err.remediation).toBeTruthy();
+      return true;
+    });
+  });
+
+  // -------------------------------------------------------------------------
+  // HTTP non-401 error (e.g. 422)
+  // -------------------------------------------------------------------------
+
+  it('throws CaServiceError on HTTP 422', async () => {
+    if (!realCsrPem) realCsrPem = await generateRealCsr();
+    makeHttpsMock(422, { message: 'Unprocessable Entity' });
+
+    await expect(service.issueCert(makeReq())).rejects.toBeInstanceOf(CaServiceError);
+  });
+
+  // -------------------------------------------------------------------------
+  // Malformed CSR — throws before HTTP call
+  // -------------------------------------------------------------------------
+
+  it('throws CaServiceError for malformed CSR without making HTTP call', async () => {
+    const requestSpy = vi.spyOn(httpsModule, 'request');
+
+    await expect(service.issueCert(makeReq({ csrPem: 'not-a-valid-csr' }))).rejects.toBeInstanceOf(
+      CaServiceError,
+    );
+
+    expect(requestSpy).not.toHaveBeenCalled();
+  });
+
+  // -------------------------------------------------------------------------
+  // Non-JSON response
+  // -------------------------------------------------------------------------
+
+  it('throws CaServiceError when step-ca returns non-JSON', async () => {
+    if (!realCsrPem) realCsrPem = await generateRealCsr();
+    makeHttpsMock(200, 'this is not json');
+
+    await expect(service.issueCert(makeReq())).rejects.toSatisfy((err: unknown) => {
+      if (!(err instanceof CaServiceError)) return false;
+      expect(err.message).toMatch(/non-JSON/);
+      return true;
+    });
+  });
+
+  // -------------------------------------------------------------------------
+  // HTTPS connection error
+  // -------------------------------------------------------------------------
+
+  it('throws CaServiceError on HTTPS connection error', async () => {
+    if (!realCsrPem) realCsrPem = await generateRealCsr();
+    makeHttpsMock(0, undefined, 'connect ECONNREFUSED 127.0.0.1:9000');
+
+    await expect(service.issueCert(makeReq())).rejects.toSatisfy((err: unknown) => {
+      if (!(err instanceof CaServiceError)) return false;
+      expect(err.message).toMatch(/HTTPS connection/);
+      expect(err.cause).toBeInstanceOf(Error);
+      return true;
+    });
+  });
+
+  // -------------------------------------------------------------------------
+  // JWT custom claims: mosaic_grant_id and mosaic_subject_user_id
+  // Verified with jose.jwtVerify for real signature verification (M6)
+  // -------------------------------------------------------------------------
+
+  it('OTT contains mosaic_grant_id, mosaic_subject_user_id, and jti; signature verifies with jose', async () => {
+    if (!realCsrPem) realCsrPem = await generateRealCsr();
+
+    let capturedBody: Record<string, unknown> | undefined;
+
+    const mockReq = {
+      write: vi.fn((data: string) => {
+        capturedBody = JSON.parse(data) as Record<string, unknown>;
+      }),
+      end: vi.fn(),
+      on: vi.fn(),
+      setTimeout: vi.fn(),
+    };
+
+    (httpsModule.request as unknown as Mock).mockImplementation(
+      (
+        _options: unknown,
+        callback: (res: {
+          statusCode: number;
+          on: (event: string, cb: (chunk?: Buffer) => void) => void;
+        }) => void,
+      ) => {
+        const mockRes = {
+          statusCode: 200,
+          on: (event: string, cb: (chunk?: Buffer) => void) => {
+            if (event === 'data') {
+              cb(Buffer.from(JSON.stringify({ crt: FAKE_CERT_PEM })));
+            }
+            if (event === 'end') {
+              cb();
+            }
+          },
+        };
+        setImmediate(() => callback(mockRes));
+        return mockReq;
+      },
+    );
+
+    await service.issueCert(makeReq({ csrPem: realCsrPem }));
+
+    expect(capturedBody).toBeDefined();
+    const ott = capturedBody!['ott'] as string;
+    expect(typeof ott).toBe('string');
+
+    // Verify JWT structure
+    const parts = ott.split('.');
+    expect(parts).toHaveLength(3);
+
+    // Decode payload without signature check first
+    const payloadJson = Buffer.from(parts[1]!, 'base64url').toString('utf8');
+    const payload = JSON.parse(payloadJson) as Record<string, unknown>;
+
+    expect(payload['mosaic_grant_id']).toBe(GRANT_ID);
+    expect(payload['mosaic_subject_user_id']).toBe(SUBJECT_USER_ID);
+    expect(typeof payload['jti']).toBe('string'); // M2: jti present
+    expect(payload['jti']).toMatch(/^[0-9a-f-]{36}$/); // UUID format
+
+    // M3: top-level sha should NOT be present; step.sha should be present
+    expect(payload['sha']).toBeUndefined();
+    const step = payload['step'] as Record<string, unknown> | undefined;
+    expect(step?.['sha']).toBeDefined();
+
+    // M6: Verify signature with jose.jwtVerify using the public key
+    const { importJWK: importJose } = await import('jose');
+    const publicKey = await importJose(TEST_EC_PUBLIC_JWK, 'ES256');
+    const verified = await jwtVerify(ott, publicKey);
+    expect(verified.payload['mosaic_grant_id']).toBe(GRANT_ID);
+  });
+
+  // -------------------------------------------------------------------------
+  // CaServiceError has cause + remediation
+  // -------------------------------------------------------------------------
+
+  it('CaServiceError carries cause and remediation', () => {
+    const cause = new Error('original error');
+    const err = new CaServiceError('something went wrong', 'fix it like this', cause);
+
+    expect(err).toBeInstanceOf(Error);
+    expect(err).toBeInstanceOf(CaServiceError);
+    expect(err.message).toBe('something went wrong');
+    expect(err.remediation).toBe('fix it like this');
+    expect(err.cause).toBe(cause);
+    expect(err.name).toBe('CaServiceError');
+  });
+
+  // -------------------------------------------------------------------------
+  // Missing crt in response
+  // -------------------------------------------------------------------------
+
+  it('throws CaServiceError when response is missing the crt field', async () => {
+    if (!realCsrPem) realCsrPem = await generateRealCsr();
+    makeHttpsMock(200, { ca: FAKE_CA_PEM });
+
+    await expect(service.issueCert(makeReq())).rejects.toSatisfy((err: unknown) => {
+      if (!(err instanceof CaServiceError)) return false;
+      expect(err.message).toMatch(/missing the "crt" field/);
+      return true;
+    });
+  });
+
+  // -------------------------------------------------------------------------
+  // M6: provisionerPassword must never appear in CaServiceError messages
+  // -------------------------------------------------------------------------
+
+  it('provisionerPassword does not appear in any CaServiceError message', async () => {
+    // Temporarily set a recognizable password to test against
+    const originalPassword = process.env['STEP_CA_PROVISIONER_PASSWORD'];
+    process.env['STEP_CA_PROVISIONER_PASSWORD'] = 'super-secret-password-12345';
+
+    // Generate a bad CSR to trigger an error path
+    const caughtErrors: CaServiceError[] = [];
+    try {
+      await service.issueCert(makeReq({ csrPem: 'not-a-csr' }));
+    } catch (err) {
+      if (err instanceof CaServiceError) {
+        caughtErrors.push(err);
+      }
+    }
+
+    // Also try HTTP 401 path
+    if (!realCsrPem) realCsrPem = await generateRealCsr();
+    makeHttpsMock(401, { message: 'Unauthorized' });
+    try {
+      await service.issueCert(makeReq({ csrPem: realCsrPem }));
+    } catch (err) {
+      if (err instanceof CaServiceError) {
+        caughtErrors.push(err);
+      }
+    }
+
+    for (const err of caughtErrors) {
+      expect(err.message).not.toContain('super-secret-password-12345');
+      if (err.remediation) {
+        expect(err.remediation).not.toContain('super-secret-password-12345');
+      }
+    }
+
+    process.env['STEP_CA_PROVISIONER_PASSWORD'] = originalPassword;
+  });
+
+  // -------------------------------------------------------------------------
+  // M7: HTTPS-only enforcement in constructor
+  // -------------------------------------------------------------------------
+
+  it('throws in constructor if STEP_CA_URL uses http://', () => {
+    const originalUrl = process.env['STEP_CA_URL'];
+    process.env['STEP_CA_URL'] = 'http://step-ca:9000';
+
+    expect(() => new CaService()).toThrow(CaServiceError);
+
+    process.env['STEP_CA_URL'] = originalUrl;
+  });
+
+  // -------------------------------------------------------------------------
+  // TTL clamp: ttlSeconds is clamped to 900 s (15 min) maximum
+  // -------------------------------------------------------------------------
+
+  it('clamps ttlSeconds to 900 s regardless of input', async () => {
+    if (!realCsrPem) realCsrPem = await generateRealCsr();
+
+    let capturedBody: Record<string, unknown> | undefined;
+
+    const mockReq = {
+      write: vi.fn((data: string) => {
+        capturedBody = JSON.parse(data) as Record<string, unknown>;
+      }),
+      end: vi.fn(),
+      on: vi.fn(),
+      setTimeout: vi.fn(),
+    };
+
+    (httpsModule.request as unknown as Mock).mockImplementation(
+      (
+        _options: unknown,
+        callback: (res: {
+          statusCode: number;
+          on: (event: string, cb: (chunk?: Buffer) => void) => void;
+        }) => void,
+      ) => {
+        const mockRes = {
+          statusCode: 200,
+          on: (event: string, cb: (chunk?: Buffer) => void) => {
+            if (event === 'data') {
+              cb(Buffer.from(JSON.stringify({ crt: FAKE_CERT_PEM })));
+            }
+            if (event === 'end') {
+              cb();
+            }
+          },
+        };
+        setImmediate(() => callback(mockRes));
+        return mockReq;
+      },
+    );
+
+    // Request 86400 s — should be clamped to 900
+    await service.issueCert(makeReq({ ttlSeconds: 86400 }));
+
+    expect(capturedBody).toBeDefined();
+    const validity = capturedBody!['validity'] as Record<string, unknown>;
+    expect(validity['duration']).toBe('900s');
+  });
+});

apps/gateway/src/federation/ca.service.ts

@@ -0,0 +1,635 @@
+/**
+ * CaService — Step-CA client for federation grant certificate issuance.
+ *
+ * Responsibilities:
+ *  1. Build a JWK-provisioner One-Time Token (OTT) signed with the provisioner
+ *     private key (ES256/ES384/RS256 per JWK kty/crv) carrying Mosaic-specific
+ *     claims (`mosaic_grant_id`, `mosaic_subject_user_id`, `step.sha`) per the
+ *     step-ca JWK provisioner protocol.
+ *  2. POST the CSR + OTT to the step-ca `/1.0/sign` endpoint over HTTPS,
+ *     pinning the trust to the CA root cert supplied via env.
+ *  3. Return an IssuedCertDto containing the leaf cert, full chain, and
+ *     serial number.
+ *
+ * Environment variables (all required at runtime — validated in constructor):
+ *   STEP_CA_URL                   https://step-ca:9000
+ *   STEP_CA_PROVISIONER_KEY_JSON  JWK provisioner private key (JSON)
+ *   STEP_CA_ROOT_CERT_PATH        Absolute path to the CA root PEM
+ *
+ * Optional (only used for JWK PBES2 decrypt at startup if key is encrypted):
+ *   STEP_CA_PROVISIONER_PASSWORD  JWK provisioner password (raw string)
+ *
+ * Custom OID registry (PRD §6, docs/federation/SETUP.md):
+ *   1.3.6.1.4.1.99999.1  — mosaic_grant_id
+ *   1.3.6.1.4.1.99999.2  — mosaic_subject_user_id
+ *
+ * Fail-loud contract:
+ *   Every error path throws CaServiceError with a human-readable `remediation`
+ *   field. Silent OID-stripping is NEVER allowed — if the sign response does
+ *   not include the cert, we throw rather than return a cert that may be
+ *   missing the custom extensions.
+ */
+
+import { Injectable, Logger } from '@nestjs/common';
+import * as crypto from 'node:crypto';
+import * as fs from 'node:fs';
+import * as https from 'node:https';
+import { SignJWT, importJWK } from 'jose';
+import { Pkcs10CertificateRequest } from '@peculiar/x509';
+import type { IssueCertRequestDto } from './ca.dto.js';
+import { IssuedCertDto } from './ca.dto.js';
+
+// ---------------------------------------------------------------------------
+// Custom error class
+// ---------------------------------------------------------------------------
+
+export class CaServiceError extends Error {
+  readonly cause: unknown;
+  readonly remediation: string;
+  readonly code?: string;
+
+  constructor(message: string, remediation: string, cause?: unknown, code?: string) {
+    super(message);
+    this.name = 'CaServiceError';
+    this.cause = cause;
+    this.remediation = remediation;
+    this.code = code;
+  }
+}
+
+// ---------------------------------------------------------------------------
+// Internal types
+// ---------------------------------------------------------------------------
+
+interface StepSignResponse {
+  crt: string;
+  ca?: string;
+  certChain?: string[];
+}
+
+interface JwkKey {
+  kty: string;
+  kid?: string;
+  use?: string;
+  alg?: string;
+  k?: string; // symmetric
+  n?: string; // RSA
+  e?: string;
+  d?: string;
+  x?: string; // EC
+  y?: string;
+  crv?: string;
+  [key: string]: unknown;
+}
+
+// ---------------------------------------------------------------------------
+// Helpers
+// ---------------------------------------------------------------------------
+
+/** UUID regex for validation */
+const UUID_RE = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i;
+
+/**
+ * Derive the JWT algorithm string from a JWK's kty/crv fields.
+ * EC P-256 → ES256, EC P-384 → ES384, RSA → RS256.
+ */
+function algFromJwk(jwk: JwkKey): string {
+  if (jwk.alg) return jwk.alg;
+  if (jwk.kty === 'EC') {
+    if (jwk.crv === 'P-384') return 'ES384';
+    return 'ES256'; // default for P-256 and Ed25519-style EC keys
+  }
+  if (jwk.kty === 'RSA') return 'RS256';
+  throw new CaServiceError(
+    `Unsupported JWK kty: ${jwk.kty}`,
+    'STEP_CA_PROVISIONER_KEY_JSON must be an EC (P-256/P-384) or RSA JWK private key.',
+  );
+}
+
+/**
+ * Compute SHA-256 fingerprint of the DER-encoded CSR body.
+ * step-ca uses this as the `step.sha` claim to bind the OTT to a specific CSR.
+ */
+function csrFingerprint(csrPem: string): string {
+  // Strip PEM headers and decode base64 body
+  const b64 = csrPem
+    .replace(/-----BEGIN CERTIFICATE REQUEST-----/, '')
+    .replace(/-----END CERTIFICATE REQUEST-----/, '')
+    .replace(/\s+/g, '');
+
+  let derBuf: Buffer;
+  try {
+    derBuf = Buffer.from(b64, 'base64');
+  } catch (err) {
+    throw new CaServiceError(
+      'Failed to base64-decode the CSR PEM body',
+      'Verify that csrPem is a valid PKCS#10 PEM-encoded certificate request.',
+      err,
+    );
+  }
+
+  if (derBuf.length === 0) {
+    throw new CaServiceError(
+      'CSR PEM decoded to empty buffer — malformed input',
+      'Provide a valid non-empty PKCS#10 PEM-encoded certificate request.',
+    );
+  }
+
+  return crypto.createHash('sha256').update(derBuf).digest('hex');
+}
+
+/**
+ * Send a JSON POST to the step-ca sign endpoint.
+ * Returns the parsed response body or throws CaServiceError.
+ */
+function httpsPost(url: string, body: unknown, agent: https.Agent): Promise<StepSignResponse> {
+  return new Promise((resolve, reject) => {
+    const bodyStr = JSON.stringify(body);
+    const parsed = new URL(url);
+
+    const options: https.RequestOptions = {
+      hostname: parsed.hostname,
+      port: parsed.port ? parseInt(parsed.port, 10) : 443,
+      path: parsed.pathname,
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+        'Content-Length': Buffer.byteLength(bodyStr),
+      },
+      agent,
+      timeout: 5000,
+    };
+
+    const req = https.request(options, (res) => {
+      const chunks: Buffer[] = [];
+      res.on('data', (chunk: Buffer) => chunks.push(chunk));
+      res.on('end', () => {
+        const raw = Buffer.concat(chunks).toString('utf8');
+
+        if (res.statusCode === 401) {
+          reject(
+            new CaServiceError(
+              `step-ca returned HTTP 401 — invalid or expired OTT`,
+              'Check STEP_CA_PROVISIONER_KEY_JSON. Ensure the mosaic-fed provisioner is configured in the CA.',
+            ),
+          );
+          return;
+        }
+
+        if (res.statusCode && res.statusCode >= 400) {
+          reject(
+            new CaServiceError(
+              `step-ca returned HTTP ${res.statusCode}: ${raw.slice(0, 256)}`,
+              `Review the step-ca logs. Status ${res.statusCode} may indicate a CSR policy violation or misconfigured provisioner.`,
+            ),
+          );
+          return;
+        }
+
+        let parsed: unknown;
+        try {
+          parsed = JSON.parse(raw) as unknown;
+        } catch (err) {
+          reject(
+            new CaServiceError(
+              'step-ca returned a non-JSON response',
+              'Verify STEP_CA_URL points to a running step-ca instance and that TLS is properly configured.',
+              err,
+            ),
+          );
+          return;
+        }
+
+        resolve(parsed as StepSignResponse);
+      });
+    });
+
+    req.setTimeout(5000, () => {
+      req.destroy(new Error('Request timed out after 5000ms'));
+    });
+
+    req.on('error', (err: Error) => {
+      reject(
+        new CaServiceError(
+          `HTTPS connection to step-ca failed: ${err.message}`,
+          'Ensure STEP_CA_URL is reachable and STEP_CA_ROOT_CERT_PATH points to the correct CA root certificate.',
+          err,
+        ),
+      );
+    });
+
+    req.write(bodyStr);
+    req.end();
+  });
+}
+
+/**
+ * Extract a decimal serial number from a PEM certificate.
+ * Throws CaServiceError on failure — never silently returns 'unknown'.
+ */
+function extractSerial(certPem: string): string {
+  let cert: crypto.X509Certificate;
+  try {
+    cert = new crypto.X509Certificate(certPem);
+  } catch (err) {
+    throw new CaServiceError(
+      'Failed to parse the issued certificate PEM',
+      'The certificate returned by step-ca could not be parsed. Check that step-ca is returning a valid PEM certificate.',
+      err,
+      'CERT_PARSE',
+    );
+  }
+  return cert.serialNumber;
+}
+
+// ---------------------------------------------------------------------------
+// Service
+// ---------------------------------------------------------------------------
+
+@Injectable()
+export class CaService {
+  private readonly logger = new Logger(CaService.name);
+
+  private readonly caUrl: string;
+  private readonly rootCertPath: string;
+  private readonly httpsAgent: https.Agent;
+  private readonly jwk: JwkKey;
+  private cachedPrivateKey: crypto.KeyObject | null = null;
+  private readonly jwtAlg: string;
+  private readonly kid: string;
+
+  constructor() {
+    const caUrl = process.env['STEP_CA_URL'];
+    const provisionerKeyJson = process.env['STEP_CA_PROVISIONER_KEY_JSON'];
+    const rootCertPath = process.env['STEP_CA_ROOT_CERT_PATH'];
+
+    if (!caUrl) {
+      throw new CaServiceError(
+        'STEP_CA_URL is not set',
+        'Set STEP_CA_URL to the base URL of the step-ca instance, e.g. https://step-ca:9000',
+      );
+    }
+
+    // Enforce HTTPS-only URL
+    let parsedUrl: URL;
+    try {
+      parsedUrl = new URL(caUrl);
+    } catch (err) {
+      throw new CaServiceError(
+        `STEP_CA_URL is not a valid URL: ${caUrl}`,
+        'Set STEP_CA_URL to a valid HTTPS URL, e.g. https://step-ca:9000',
+        err,
+      );
+    }
+    if (parsedUrl.protocol !== 'https:') {
+      throw new CaServiceError(
+        `STEP_CA_URL must use HTTPS — got: ${parsedUrl.protocol}`,
+        'Set STEP_CA_URL to an https:// URL. Unencrypted connections to the CA are not permitted.',
+      );
+    }
+
+    if (!provisionerKeyJson) {
+      throw new CaServiceError(
+        'STEP_CA_PROVISIONER_KEY_JSON is not set',
+        'Set STEP_CA_PROVISIONER_KEY_JSON to the JSON-encoded JWK for the mosaic-fed provisioner.',
+      );
+    }
+    if (!rootCertPath) {
+      throw new CaServiceError(
+        'STEP_CA_ROOT_CERT_PATH is not set',
+        'Set STEP_CA_ROOT_CERT_PATH to the absolute path of the step-ca root CA certificate PEM file.',
+      );
+    }
+
+    // Parse JWK once — do NOT store the raw JSON string as a class field
+    let jwk: JwkKey;
+    try {
+      jwk = JSON.parse(provisionerKeyJson) as JwkKey;
+    } catch (err) {
+      throw new CaServiceError(
+        'STEP_CA_PROVISIONER_KEY_JSON is not valid JSON',
+        'Set STEP_CA_PROVISIONER_KEY_JSON to the JSON-serialised JWK object for the mosaic-fed provisioner.',
+        err,
+      );
+    }
+
+    // Derive algorithm from JWK metadata
+    const jwtAlg = algFromJwk(jwk);
+    const kid = jwk.kid ?? 'mosaic-fed';
+
+    // Import the JWK into a native KeyObject — fail loudly if it cannot be loaded.
+    // We do this synchronously here by calling the async importJWK via a blocking workaround.
+    // Actually importJWK is async, so we store it for use during token building.
+    // We keep the raw jwk object for later async import inside buildOtt.
+    // NOTE: We do NOT store provisionerKeyJson string as a class field.
+    this.jwk = jwk;
+    this.jwtAlg = jwtAlg;
+    this.kid = kid;
+
+    this.caUrl = caUrl;
+    this.rootCertPath = rootCertPath;
+
+    // Read the root cert and pin it for all HTTPS connections.
+    let rootCert: string;
+    try {
+      rootCert = fs.readFileSync(this.rootCertPath, 'utf8');
+    } catch (err) {
+      throw new CaServiceError(
+        `Cannot read STEP_CA_ROOT_CERT_PATH: ${rootCertPath}`,
+        'Ensure the file exists and is readable by the gateway process.',
+        err,
+      );
+    }
+
+    this.httpsAgent = new https.Agent({
+      ca: rootCert,
+      rejectUnauthorized: true,
+    });
+
+    this.logger.log(`CaService initialised — CA URL: ${this.caUrl}`);
+  }
+
+  /**
+   * Lazily import the private key from JWK on first use.
+   * The key is cached in cachedPrivateKey after first import.
+   */
+  private async getPrivateKey(): Promise<crypto.KeyObject> {
+    if (this.cachedPrivateKey !== null) return this.cachedPrivateKey;
+    try {
+      const key = await importJWK(this.jwk, this.jwtAlg);
+      // importJWK returns KeyLike (crypto.KeyObject | Uint8Array) — in Node.js it's KeyObject
+      this.cachedPrivateKey = key as unknown as crypto.KeyObject;
+      return this.cachedPrivateKey;
+    } catch (err) {
+      throw new CaServiceError(
+        'Failed to import STEP_CA_PROVISIONER_KEY_JSON as a cryptographic key',
+        'Ensure STEP_CA_PROVISIONER_KEY_JSON contains a valid JWK private key (EC P-256/P-384 or RSA).',
+        err,
+      );
+    }
+  }
+
+  /**
+   * Build the JWK-provisioner OTT signed with the provisioner private key.
+   * Algorithm is derived from the JWK kty/crv fields.
+   */
+  private async buildOtt(params: {
+    csrPem: string;
+    grantId: string;
+    subjectUserId: string;
+    ttlSeconds: number;
+    csrCn: string;
+  }): Promise<string> {
+    const { csrPem, grantId, subjectUserId, ttlSeconds, csrCn } = params;
+
+    // Validate UUID shape for grant id and subject user id
+    if (!UUID_RE.test(grantId)) {
+      throw new CaServiceError(
+        `grantId is not a valid UUID: ${grantId}`,
+        'Provide a valid UUID (RFC 4122) for grantId.',
+        undefined,
+        'INVALID_GRANT_ID',
+      );
+    }
+    if (!UUID_RE.test(subjectUserId)) {
+      throw new CaServiceError(
+        `subjectUserId is not a valid UUID: ${subjectUserId}`,
+        'Provide a valid UUID (RFC 4122) for subjectUserId.',
+        undefined,
+        'INVALID_GRANT_ID',
+      );
+    }
+
+    const sha = csrFingerprint(csrPem);
+    const now = Math.floor(Date.now() / 1000);
+    const privateKey = await this.getPrivateKey();
+
+    const ott = await new SignJWT({
+      iss: this.kid,
+      sub: csrCn, // M1: set sub to identity from CSR CN
+      aud: [`${this.caUrl}/1.0/sign`],
+      iat: now,
+      nbf: now - 30, // 30 s clock-skew tolerance
+      exp: now + Math.min(ttlSeconds, 3600), // OTT validity ≤ 1 h
+      jti: crypto.randomUUID(), // M2: unique token ID
+      // step.sha is the canonical field name used in the template — M3: keep only step.sha
+      step: { sha },
+      // Mosaic custom claims consumed by federation.tpl
+      mosaic_grant_id: grantId,
+      mosaic_subject_user_id: subjectUserId,
+    })
+      .setProtectedHeader({ alg: this.jwtAlg, typ: 'JWT', kid: this.kid })
+      .sign(privateKey);
+
+    return ott;
+  }
+
+  /**
+   * Validate a PEM-encoded CSR using @peculiar/x509.
+   * Verifies the self-signature, key type/size, and signature algorithm.
+   * Optionally verifies that the CSR's SANs match the expected set.
+   *
+   * Throws CaServiceError with code 'INVALID_CSR' on failure.
+   */
+  private async validateCsr(pem: string, expectedSans?: string[]): Promise<string> {
+    let csr: Pkcs10CertificateRequest;
+    try {
+      csr = new Pkcs10CertificateRequest(pem);
+    } catch (err) {
+      throw new CaServiceError(
+        'Failed to parse CSR PEM as a valid PKCS#10 certificate request',
+        'Provide a valid PEM-encoded PKCS#10 CSR.',
+        err,
+        'INVALID_CSR',
+      );
+    }
+
+    // Verify self-signature
+    let valid: boolean;
+    try {
+      valid = await csr.verify();
+    } catch (err) {
+      throw new CaServiceError(
+        'CSR signature verification threw an error',
+        'The CSR self-signature could not be verified. Ensure the CSR is properly formed.',
+        err,
+        'INVALID_CSR',
+      );
+    }
+    if (!valid) {
+      throw new CaServiceError(
+        'CSR self-signature is invalid',
+        'The CSR must be self-signed with the corresponding private key.',
+        undefined,
+        'INVALID_CSR',
+      );
+    }
+
+    // Validate signature algorithm — reject MD5 and SHA-1
+    // signatureAlgorithm is HashedAlgorithm which extends Algorithm.
+    // Cast through unknown to access .name and .hash.name without DOM lib globals.
+    const sigAlgAny = csr.signatureAlgorithm as unknown as {
+      name?: string;
+      hash?: { name?: string };
+    };
+    const sigAlgName = (sigAlgAny.name ?? '').toLowerCase();
+    const hashName = (sigAlgAny.hash?.name ?? '').toLowerCase();
+    if (
+      sigAlgName.includes('md5') ||
+      sigAlgName.includes('sha1') ||
+      hashName === 'sha-1' ||
+      hashName === 'sha1'
+    ) {
+      throw new CaServiceError(
+        `CSR uses a forbidden signature algorithm: ${sigAlgAny.name ?? 'unknown'}`,
+        'Use SHA-256 or stronger. MD5 and SHA-1 are not permitted.',
+        undefined,
+        'INVALID_CSR',
+      );
+    }
+
+    // Validate public key algorithm and strength via the algorithm descriptor on the key.
+    // csr.publicKey.algorithm is type Algorithm (WebCrypto) — use name-based checks.
+    // We cast to an extended interface to access curve/modulus info without DOM globals.
+    const pubKeyAlgo = csr.publicKey.algorithm as {
+      name: string;
+      namedCurve?: string;
+      modulusLength?: number;
+    };
+    const keyAlgoName = pubKeyAlgo.name;
+
+    if (keyAlgoName === 'RSASSA-PKCS1-v1_5' || keyAlgoName === 'RSA-PSS') {
+      const modulusLength = pubKeyAlgo.modulusLength ?? 0;
+      if (modulusLength < 2048) {
+        throw new CaServiceError(
+          `CSR RSA key is too short: ${modulusLength} bits (minimum 2048)`,
+          'Use an RSA key of at least 2048 bits.',
+          undefined,
+          'INVALID_CSR',
+        );
+      }
+    } else if (keyAlgoName === 'ECDSA') {
+      const namedCurve = pubKeyAlgo.namedCurve ?? '';
+      const allowedCurves = new Set(['P-256', 'P-384']);
+      if (!allowedCurves.has(namedCurve)) {
+        throw new CaServiceError(
+          `CSR EC key uses disallowed curve: ${namedCurve}`,
+          'Use EC P-256 or P-384. Other curves are not permitted.',
+          undefined,
+          'INVALID_CSR',
+        );
+      }
+    } else if (keyAlgoName === 'Ed25519') {
+      // Ed25519 is explicitly allowed
+    } else {
+      throw new CaServiceError(
+        `CSR uses unsupported key algorithm: ${keyAlgoName}`,
+        'Use EC (P-256/P-384), Ed25519, or RSA (≥2048 bit) keys.',
+        undefined,
+        'INVALID_CSR',
+      );
+    }
+
+    // Extract SANs if expectedSans provided
+    if (expectedSans && expectedSans.length > 0) {
+      // Get SANs from CSR extensions
+      const sanExtension = csr.extensions?.find(
+        (ext) => ext.type === '2.5.29.17', // Subject Alternative Name OID
+      );
+      const csrSans: string[] = [];
+      if (sanExtension) {
+        // Parse the raw SAN extension — store as stringified for comparison
+        // @peculiar/x509 exposes SANs through the parsed extension
+        const sanExt = sanExtension as { names?: Array<{ type: string; value: string }> };
+        if (sanExt.names) {
+          for (const name of sanExt.names) {
+            csrSans.push(name.value);
+          }
+        }
+      }
+
+      const csrSanSet = new Set(csrSans);
+      const expectedSanSet = new Set(expectedSans);
+      const missing = expectedSans.filter((s) => !csrSanSet.has(s));
+      const extra = csrSans.filter((s) => !expectedSanSet.has(s));
+
+      if (missing.length > 0 || extra.length > 0) {
+        throw new CaServiceError(
+          `CSR SANs do not match expected set. Missing: [${missing.join(', ')}], Extra: [${extra.join(', ')}]`,
+          'The CSR must include exactly the SANs specified in the issuance request.',
+          undefined,
+          'INVALID_CSR',
+        );
+      }
+    }
+
+    // Return the CN from the CSR subject for use as JWT sub
+    const cn = csr.subjectName.getField('CN')?.[0] ?? '';
+    return cn;
+  }
+
+  /**
+   * Submit a CSR to step-ca and return the issued certificate.
+   *
+   * Throws `CaServiceError` on any failure (network, auth, malformed input).
+   * Never silently swallows errors — fail-loud is a hard contract per M2-02 review.
+   */
+  async issueCert(req: IssueCertRequestDto): Promise<IssuedCertDto> {
+    // Clamp TTL to 15-minute maximum (H2)
+    const ttl = Math.min(req.ttlSeconds ?? 300, 900);
+
+    this.logger.debug(
+      `issueCert — grantId=${req.grantId} subjectUserId=${req.subjectUserId} ttl=${ttl}s`,
+    );
+
+    // Validate CSR — real cryptographic validation (H3)
+    const csrCn = await this.validateCsr(req.csrPem);
+
+    const ott = await this.buildOtt({
+      csrPem: req.csrPem,
+      grantId: req.grantId,
+      subjectUserId: req.subjectUserId,
+      ttlSeconds: ttl,
+      csrCn,
+    });
+
+    const signUrl = `${this.caUrl}/1.0/sign`;
+    const requestBody = {
+      csr: req.csrPem,
+      ott,
+      validity: {
+        duration: `${ttl}s`,
+      },
+    };
+
+    this.logger.debug(`Posting CSR to ${signUrl}`);
+    const response = await httpsPost(signUrl, requestBody, this.httpsAgent);
+
+    if (!response.crt) {
+      throw new CaServiceError(
+        'step-ca sign response missing the "crt" field',
+        'This is unexpected — the step-ca instance may be misconfigured or running an incompatible version.',
+      );
+    }
+
+    // Build certChainPem: prefer certChain array, fall back to ca field, fall back to crt alone.
+    let certChainPem: string;
+    if (response.certChain && response.certChain.length > 0) {
+      certChainPem = response.certChain.join('\n');
+    } else if (response.ca) {
+      certChainPem = response.crt + '\n' + response.ca;
+    } else {
+      certChainPem = response.crt;
+    }
+
+    const serialNumber = extractSerial(response.crt);
+
+    this.logger.log(`Certificate issued — serial=${serialNumber} grantId=${req.grantId}`);
+
+    const result = new IssuedCertDto();
+    result.certPem = response.crt;
+    result.certChainPem = certChainPem;
+    result.serialNumber = serialNumber;
+    return result;
+  }
+}

apps/gateway/src/federation/federation.module.ts

@@ -0,0 +1,8 @@
+import { Module } from '@nestjs/common';
+import { CaService } from './ca.service.js';
+
+@Module({
+  providers: [CaService],
+  exports: [CaService],
+})
+export class FederationModule {}