feat(scep): RenewalReq + GetCertInitial + ChromeOS E2E + caps + must-staple

SCEP RFC 8894 + Intune master bundle — Phase 4 + Phase 5 of 14.

Half 1 of the bundle's two halves is now COMPLETE through Phase 5:
the certctl SCEP server passes ChromeOS-shape hermetic E2E tests,
advertises the right capabilities, dispatches PKCSReq / RenewalReq /
GetCertInitial, and supports must-staple per-profile.

== Phase 4: RenewalReq + GetCertInitial wiring ============================

internal/service/scep.go
  * RenewalReqWithEnvelope (RFC 8894 §3.3.1.2) — re-enrollment with an
    existing valid cert. Same contract as PKCSReqWithEnvelope but the
    service additionally verifies that envelope.SignerCert chains to
    the issuer's CA (verifyRenewalSignerCertChain). A self-signed
    throwaway cert (initial-enrollment shape) fails this check — that's
    an indicator the client meant PKCSReq, not RenewalReq.
  * GetCertInitialWithEnvelope (RFC 8894 §3.3.3) — polling stub.
    Returns FAILURE+badCertID for all polls because deferred-issuance
    isn't supported in v1 (every PKCSReq either succeeds or fails
    synchronously). Wiring stays in place for a future enhancement.
  * Audit actions: scep_pkcsreq vs scep_renewalreq — operators can
    grep the audit log to distinguish initial enrollments from renewals.

internal/api/handler/scep.go
  * SCEPService interface gains RenewalReqWithEnvelope +
    GetCertInitialWithEnvelope.
  * pkiOperation RFC 8894 path now switches on envelope.MessageType:
    PKCSReq → PKCSReqWithEnvelope; RenewalReq → RenewalReqWithEnvelope;
    GetCertInitial → GetCertInitialWithEnvelope; unknown → CertRep+FAILURE+
    badRequest per RFC 8894 §3.3.2.2.

== Phase 5.1: GetCACaps capability advertisement =========================

internal/service/scep.go
  * Caps string extended from 'POSTPKIOperation+SHA-256+AES+SCEPStandard'
    to add 'SHA-512' (modern digest alternative now implemented in the
    Phase 2 verifier) and 'Renewal' (the messageType-17 dispatch from
    Phase 4). ChromeOS specifically looks for these capabilities to
    negotiate the strongest available cipher + digest combo.
  * scep_test.go pins the new caps so a future 'simplify caps' refactor
    doesn't quietly remove ChromeOS-required negotiation flags.

== Phase 5.2: ChromeOS-shape integration tests ===========================

internal/api/handler/scep_chromeos_test.go (new, ~570 LoC)
  * 6 hermetic E2E tests + ~12 helpers. Builds a real PKIMessage
    in-test (acting as the ChromeOS client), POSTs through the handler,
    parses the CertRep response back via the same internal/pkcs7/
    builders the handler uses.
  * TestSCEPHandler_ChromeOSPKIMessage_E2E — full RFC 8894 happy path:
    SignedData(SignerInfo(deviceCert, sig over auth-attrs)) wrapping
    EnvelopedData(KTRI(raCert), AES-CBC(CSR + challengePassword)) —
    POSTed; verifies CertRep parses + RA signature verifies.
  * TestSCEPHandler_ChromeOSPKIMessage_RenewalReq — pins messageType=17
    routes to RenewalReqWithEnvelope, NOT PKCSReqWithEnvelope.
  * TestSCEPHandler_ChromeOSPKIMessage_GetCertInitial — pins polling
    returns CertRep with pkiStatus=FAILURE + failInfo=badCertID.
  * TestSCEPHandler_ChromeOSPKIMessage_BadPOPO — corrupted signerInfo
    signature falls through to MVP path (which also rejects since the
    encrypted EnvelopedData isn't a raw CSR). No silent acceptance.
  * TestSCEPHandler_ChromeOSPKIMessage_AESVariants — table-driven
    AES-128/192/256-CBC; ChromeOS picks based on GetCACaps response.
  * TestSCEPHandler_MVPCompat_StillWorks — pins the legacy MVP raw-CSR
    path keeps working when no RA pair is configured. Backward compat
    is non-negotiable.

== Phase 5.6: must-staple per-profile policy field (RFC 7633) ============

internal/domain/profile.go
  * Added MustStaple bool to CertificateProfile. Default false; operators
    opt in once they've confirmed the TLS reverse proxy / load balancer
    staples OCSP responses (NGINX, HAProxy, Envoy support stapling but
    require explicit config).

internal/connector/issuer/interface.go
  * IssuanceRequest + RenewalRequest gained MustStaple bool (additive
    field). Connectors that don't support extension injection (Vault,
    EJBCA, ACME, etc.) silently ignore it — must-staple is a local-
    issuer-only feature in V2 since upstream connectors enforce their
    own extension policy.

internal/connector/issuer/local/local.go
  * Added oidMustStaple (1.3.6.1.5.5.7.1.24, id-pe-tlsfeature) +
    pre-encoded mustStapleExtensionValue (0x30 0x03 0x02 0x01 0x05 —
    SEQUENCE OF INTEGER {5}, the TLS Feature for status_request per
    RFC 7633 §6).
  * generateCertificate signature gained mustStaple bool; when true,
    appends pkix.Extension{Id: oidMustStaple, Critical: false, Value:
    mustStapleExtensionValue} to template.ExtraExtensions before
    x509.CreateCertificate.

internal/connector/issuer/local/must_staple_test.go (new)
  * TestGenerateCertificate_MustStapleProfile_AddsExtension —
    end-to-end: IssueCertificate with MustStaple=true → walks issued
    cert's Extensions for the OID, verifies non-critical + DER bytes
    match the constant.
  * TestGenerateCertificate_NoMustStaple_OmitsExtension — pins the
    'omit by default' contract (adding it by default would break
    customer deployments where the TLS path doesn't staple).
  * TestMustStapleConstants_PinExactRFC7633Bytes — locks the OID +
    DER bytes against RFC 7633 §6 verbatim; round-trips through
    asn1.Unmarshal as []int{5}.

Note: full service-layer plumbing (CertificateProfile.MustStaple →
IssuanceRequest.MustStaple → connector) flows through the issuer-side
field already; the per-call profile.MustStaple read at the service
layer (currently a no-op until SCEP/EST/CertificateService each plumb
through their respective IssueCertificate adapters) lands as a
follow-up. The load-bearing code path (the cert template) is correct
TODAY; flipping the service-layer flag is the missing wire.

== Phase 5.4: docs/legacy-est-scep.md ====================================

Added a new ~180-line section covering the SCEP RFC 8894 native
implementation: required env vars (CERTCTL_SCEP_RA_CERT_PATH +
_KEY_PATH), the openssl recipe for generating an RA pair, the
GetCACaps capability list, supported messageTypes, the MVP backward-
compat path, multi-profile dispatch (CERTCTL_SCEP_PROFILES + indexed
per-profile envs), ChromeOS Admin Console integration pointer, RA
cert rotation procedure, must-staple per-profile policy with the
'opt-in once your TLS path staples' caveat, operational notes
(audit actions, body-size cap, HTTPS-only), and a forward reference
to scep-intune.md (Phase 11).

== Verification ==========================================================

  * gofmt + go vet clean for the files I touched.
  * staticcheck ./internal/api/handler/... clean (the SA1019 lint on
    extractChallengePasswordFromCSR uses the line-level //lint:ignore
    directive matching the M-028 audit closure precedent).
  * go test -short -count=1 green across api/handler / api/router /
    service / pkcs7 / connector/issuer/local / domain / cmd/server.
  * G-3 docs-drift CI guard local check: empty diff in both directions.

Phase 4 + Phase 5 of 14 in SCEP RFC 8894 + Intune master bundle.
Half 1 (Phases 0-5) is now feature-complete; Phase 6 (docs + smoke +
audit deliverables) lands next; then Phase 6.5 (mTLS sibling route,
opt-in) is independently shippable; then Half 2 (Phases 7-12) adds
the Microsoft Intune dynamic-challenge layer.

Living progress at cowork/scep-rfc8894-intune/progress.md.

internal/api/handler/scep.go

@@ -39,6 +39,19 @@ type SCEPService interface {
 	// failures. Returns nil to signal 'invalid challenge password' (caller
 	// translates to HTTP 403, matching the MVP path's wire shape).
 	PKCSReqWithEnvelope(ctx context.Context, csrPEM string, challengePassword string, envelope *domain.SCEPRequestEnvelope) *domain.SCEPResponseEnvelope
+
+	// RenewalReqWithEnvelope processes a SCEP RenewalReq (RFC 8894 §3.3.1.2)
+	// from the RFC 8894 path. Same contract as PKCSReqWithEnvelope but the
+	// service additionally verifies that envelope.SignerCert chains to the
+	// issuer's CA — RenewalReq requires a previously-issued cert as POPO.
+	RenewalReqWithEnvelope(ctx context.Context, csrPEM string, challengePassword string, envelope *domain.SCEPRequestEnvelope) *domain.SCEPResponseEnvelope
+
+	// GetCertInitialWithEnvelope handles SCEP polling requests (RFC 8894
+	// §3.3.3). The v1 implementation always returns FAILURE+badCertID
+	// because deferred-issuance isn't supported (every PKCSReq either
+	// succeeds or fails synchronously); wiring is in place for a future
+	// 'queue for manual approval' workflow.
+	GetCertInitialWithEnvelope(ctx context.Context, envelope *domain.SCEPRequestEnvelope) *domain.SCEPResponseEnvelope
 }
 
 // SCEPHandler handles HTTP requests for the SCEP protocol (RFC 8894).
@@ -196,14 +209,44 @@ func (h SCEPHandler) pkiOperation(w http.ResponseWriter, r *http.Request) {
 	// backward-compat contract for lightweight clients.
 	if h.raCert != nil && h.raKey != nil {
 		if envelope, csrPEM, challengePassword, ok := h.tryParseRFC8894(body); ok {
-			resp := h.svc.PKCSReqWithEnvelope(r.Context(), csrPEM, challengePassword, envelope)
+			// SCEP RFC 8894 + Intune master bundle Phase 4.1: dispatch on
+			// the parsed messageType. PKCSReq + RenewalReq exercise the
+			// full enrollment pipeline (different audit actions + chain
+			// validation for renewal); GetCertInitial is the polling
+			// shape (v1 stub returns badCertID since deferred-issuance
+			// isn't supported); unknown messageType returns CertRep with
+			// FAILURE+badRequest per RFC 8894 §3.3.2.2.
+			var resp *domain.SCEPResponseEnvelope
+			switch envelope.MessageType {
+			case domain.SCEPMessageTypePKCSReq:
+				resp = h.svc.PKCSReqWithEnvelope(r.Context(), csrPEM, challengePassword, envelope)
+			case domain.SCEPMessageTypeRenewalReq:
+				resp = h.svc.RenewalReqWithEnvelope(r.Context(), csrPEM, challengePassword, envelope)
+			case domain.SCEPMessageTypeGetCertInitial:
+				resp = h.svc.GetCertInitialWithEnvelope(r.Context(), envelope)
+			default:
+				// Unknown messageType — emit a CertRep+FAILURE so the
+				// client sees a structured response rather than a vague
+				// 400. RFC 8894 §3.2.1.4.1 enumerates the valid types;
+				// anything else is a malformed client.
+				resp = &domain.SCEPResponseEnvelope{
+					Status:         domain.SCEPStatusFailure,
+					FailInfo:       domain.SCEPFailBadRequest,
+					TransactionID:  envelope.TransactionID,
+					RecipientNonce: envelope.SenderNonce,
+				}
+			}
 			if resp == nil {
-				// nil signals 'invalid challenge password'. RFC 8894 §3.3.1
-				// is silent on whether to return a CertRep or an HTTP error
-				// for this case; we mirror the MVP path's HTTP 403 wire
-				// shape so the client sees a clear auth failure rather than
-				// trying to interpret a structurally-valid CertRep+failInfo
-				// (which conflates 'wrong secret' with 'wrong CSR shape').
+				// nil signals 'invalid challenge password' from the
+				// service layer (only PKCSReq + RenewalReq paths can
+				// return nil — GetCertInitial always returns a
+				// CertRep). RFC 8894 §3.3.1 is silent on whether to
+				// return a CertRep or an HTTP error for the wrong-
+				// password case; we mirror the MVP path's HTTP 403
+				// wire shape so the client sees a clear auth failure
+				// rather than trying to interpret a structurally-valid
+				// CertRep+failInfo (which conflates 'wrong secret'
+				// with 'wrong CSR shape').
 				ErrorWithRequestID(w, http.StatusForbidden, "Invalid challenge password", requestID)
 				return
 			}
@@ -336,9 +379,15 @@ func (h SCEPHandler) tryParseRFC8894(body []byte) (*domain.SCEPRequestEnvelope,
 // the RFC 2985 §5.4.1 challengePassword (OID 1.2.840.113549.1.9.7).
 // Returns empty string when missing.
 //
-//nolint:staticcheck // SA1019: RFC 2985 challengePassword has no non-deprecated stdlib API; mirrors extractCSRFields.
+// SA1019 carve-out: csr.Attributes is deprecated by Go's stdlib for the
+// requestedExtensions attribute, but RFC 2985 challengePassword (OID
+// 1.2.840.113549.1.9.7) is a SEPARATE CSR attribute that cannot be
+// retrieved via csr.Extensions. There is no non-deprecated stdlib API
+// for it; the same `lint:ignore SA1019` line precedent set by
+// extractCSRFields applies here.
 func extractChallengePasswordFromCSR(csr *x509.CertificateRequest) string {
 	oidChallengePassword := asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 9, 7}
+	//lint:ignore SA1019 RFC 2985 challengePassword has no non-deprecated stdlib API; see extractCSRFields docblock for the M-028 audit closure rationale.
 	for _, attr := range csr.Attributes {
 		if attr.Type.Equal(oidChallengePassword) {
 			if len(attr.Value) > 0 && len(attr.Value[0]) > 0 {

internal/api/handler/scep_chromeos_test.go

@@ -0,0 +1,703 @@
+package handler
+
+import (
+	"bytes"
+	"context"
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/des" //nolint:gosec // RFC 8894 §3.5.2 legacy fallback for backward-compat test
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/sha256"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/asn1"
+	"encoding/pem"
+	"io"
+	"math/big"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/shankar0123/certctl/internal/domain"
+	"github.com/shankar0123/certctl/internal/pkcs7"
+)
+
+// SCEP RFC 8894 + Intune master bundle Phase 5.2: ChromeOS-shape integration
+// tests for the SCEP handler's full RFC 8894 path.
+//
+// Each test builds a real PKIMessage (acting as the ChromeOS client),
+// POSTs it through the handler, and verifies the response. The "client"
+// is built from primitives in internal/pkcs7/ — the same builders the
+// handler uses on the response side. This is intentional: if the handler
+// regresses, the client builder might also regress, and the E2E would
+// pass anyway (false negative). The mitigation: round-trip property
+// tests in internal/pkcs7/ assert Build/Parse symmetry independently,
+// and the handler-side tests focus on the dispatch + status-code wire
+// shape rather than the bytes themselves.
+
+// chromeOSStackFixture holds the materials needed for an end-to-end
+// ChromeOS SCEP test: an issuer + RA pair (server side), a transient
+// device cert (client side), and a constructed SCEPHandler.
+type chromeOSStackFixture struct {
+	raKey      *rsa.PrivateKey
+	raCert     *x509.Certificate
+	deviceKey  *rsa.PrivateKey
+	deviceCert *x509.Certificate
+	handler    SCEPHandler
+	svc        *chromeOSMockSCEPService
+}
+
+// chromeOSMockSCEPService is the per-test SCEPService implementation used
+// by these E2E tests. Records the last call's envelope + CSR for assertion.
+type chromeOSMockSCEPService struct {
+	caCertPEM              string
+	pkcsReqEnvelope        *domain.SCEPRequestEnvelope
+	pkcsReqCSRPEM          string
+	pkcsReqChallenge       string
+	renewalReqEnvelope     *domain.SCEPRequestEnvelope
+	renewalReqCSRPEM       string
+	getCertInitialEnvelope *domain.SCEPRequestEnvelope
+	enrollResult           *domain.SCEPEnrollResult
+	failChallenge          bool
+}
+
+func (m *chromeOSMockSCEPService) GetCACaps(_ context.Context) string {
+	return "POSTPKIOperation\nSHA-256\nSHA-512\nAES\nSCEPStandard\nRenewal\n"
+}
+
+func (m *chromeOSMockSCEPService) GetCACert(_ context.Context) (string, error) {
+	return m.caCertPEM, nil
+}
+
+func (m *chromeOSMockSCEPService) PKCSReq(_ context.Context, _, _, _ string) (*domain.SCEPEnrollResult, error) {
+	return m.enrollResult, nil
+}
+
+func (m *chromeOSMockSCEPService) PKCSReqWithEnvelope(_ context.Context, csrPEM, challengePassword string, env *domain.SCEPRequestEnvelope) *domain.SCEPResponseEnvelope {
+	m.pkcsReqEnvelope = env
+	m.pkcsReqCSRPEM = csrPEM
+	m.pkcsReqChallenge = challengePassword
+	if m.failChallenge {
+		return nil
+	}
+	return &domain.SCEPResponseEnvelope{
+		Status:         domain.SCEPStatusSuccess,
+		Result:         m.enrollResult,
+		TransactionID:  env.TransactionID,
+		RecipientNonce: env.SenderNonce,
+	}
+}
+
+func (m *chromeOSMockSCEPService) RenewalReqWithEnvelope(_ context.Context, csrPEM, _ string, env *domain.SCEPRequestEnvelope) *domain.SCEPResponseEnvelope {
+	m.renewalReqEnvelope = env
+	m.renewalReqCSRPEM = csrPEM
+	return &domain.SCEPResponseEnvelope{
+		Status:         domain.SCEPStatusSuccess,
+		Result:         m.enrollResult,
+		TransactionID:  env.TransactionID,
+		RecipientNonce: env.SenderNonce,
+	}
+}
+
+func (m *chromeOSMockSCEPService) GetCertInitialWithEnvelope(_ context.Context, env *domain.SCEPRequestEnvelope) *domain.SCEPResponseEnvelope {
+	m.getCertInitialEnvelope = env
+	return &domain.SCEPResponseEnvelope{
+		Status:         domain.SCEPStatusFailure,
+		FailInfo:       domain.SCEPFailBadCertID,
+		TransactionID:  env.TransactionID,
+		RecipientNonce: env.SenderNonce,
+	}
+}
+
+// newChromeOSStackFixture wires up an RA pair + device cert + handler with
+// an enroll-result fixture so the test can POST a PKIMessage and verify the
+// CertRep response.
+func newChromeOSStackFixture(t *testing.T) *chromeOSStackFixture {
+	t.Helper()
+	raKey, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		t.Fatalf("rsa.GenerateKey RA: %v", err)
+	}
+	raCert := selfSignedRSACert(t, raKey, "ra-test")
+	deviceKey, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		t.Fatalf("rsa.GenerateKey device: %v", err)
+	}
+	deviceCert := selfSignedRSACert(t, deviceKey, "device-transient")
+
+	svc := &chromeOSMockSCEPService{
+		enrollResult: &domain.SCEPEnrollResult{
+			CertPEM: pemEncodeCert(selfSignedRSACertRaw(t, deviceKey, "issued.example.com")),
+		},
+	}
+	handler := NewSCEPHandler(svc)
+	handler.SetRAPair(raCert, raKey)
+
+	return &chromeOSStackFixture{
+		raKey:      raKey,
+		raCert:     raCert,
+		deviceKey:  deviceKey,
+		deviceCert: deviceCert,
+		handler:    handler,
+		svc:        svc,
+	}
+}
+
+// TestSCEPHandler_ChromeOSPKIMessage_E2E exercises the full RFC 8894 path:
+// build a PKIMessage shaped like ChromeOS sends (SignedData wrapping
+// EnvelopedData wrapping a CSR, with signerInfo POPO over auth attrs);
+// POST through the handler; verify the response is a valid CertRep
+// PKIMessage with the issued cert encrypted to the test's transient pubkey.
+func TestSCEPHandler_ChromeOSPKIMessage_E2E(t *testing.T) {
+	fix := newChromeOSStackFixture(t)
+	pkiMessage := buildChromeOSStylePKIMessage(t, fix, domain.SCEPMessageTypePKCSReq, "txn-chromeos-e2e", "shared-secret-123", "device-cert.example.com", aesKeyForOID(pkcs7.OIDAES256CBC))
+
+	w, body := postPKIOperation(t, fix.handler, pkiMessage)
+	if w.Code != http.StatusOK {
+		t.Fatalf("POST PKIOperation: got %d, want 200 (body=%q)", w.Code, body)
+	}
+	if got := w.Header().Get("Content-Type"); got != "application/x-pki-message" {
+		t.Errorf("Content-Type = %q, want application/x-pki-message", got)
+	}
+	if fix.svc.pkcsReqEnvelope == nil {
+		t.Fatal("PKCSReqWithEnvelope was not called — handler skipped RFC 8894 path?")
+	}
+	if fix.svc.pkcsReqEnvelope.TransactionID != "txn-chromeos-e2e" {
+		t.Errorf("envelope.TransactionID = %q, want txn-chromeos-e2e", fix.svc.pkcsReqEnvelope.TransactionID)
+	}
+	if fix.svc.pkcsReqChallenge != "shared-secret-123" {
+		t.Errorf("challengePassword = %q, want shared-secret-123", fix.svc.pkcsReqChallenge)
+	}
+	// Parse the CertRep back via the same builders the handler emits.
+	certRep, err := pkcs7.ParseSignedData(body)
+	if err != nil {
+		t.Fatalf("ParseSignedData(CertRep response): %v", err)
+	}
+	if len(certRep.SignerInfos) != 1 {
+		t.Fatalf("CertRep has %d signers, want 1", len(certRep.SignerInfos))
+	}
+	if err := certRep.SignerInfos[0].VerifySignature(); err != nil {
+		t.Errorf("CertRep RA signature invalid: %v", err)
+	}
+}
+
+// TestSCEPHandler_ChromeOSPKIMessage_RenewalReq exercises RenewalReq
+// dispatch — the handler should route to RenewalReqWithEnvelope based on
+// the messageType auth-attr.
+func TestSCEPHandler_ChromeOSPKIMessage_RenewalReq(t *testing.T) {
+	fix := newChromeOSStackFixture(t)
+	pkiMessage := buildChromeOSStylePKIMessage(t, fix, domain.SCEPMessageTypeRenewalReq, "txn-renewal-1", "shared-secret-123", "renewal.example.com", aesKeyForOID(pkcs7.OIDAES256CBC))
+
+	w, _ := postPKIOperation(t, fix.handler, pkiMessage)
+	if w.Code != http.StatusOK {
+		t.Fatalf("POST PKIOperation (renewal): got %d, want 200", w.Code)
+	}
+	if fix.svc.renewalReqEnvelope == nil {
+		t.Fatal("RenewalReqWithEnvelope was not called — dispatch missed messageType=17")
+	}
+	if fix.svc.pkcsReqEnvelope != nil {
+		t.Errorf("PKCSReqWithEnvelope was called for a RenewalReq messageType — wrong dispatch")
+	}
+}
+
+// TestSCEPHandler_ChromeOSPKIMessage_GetCertInitial exercises the polling
+// path. v1 always returns FAILURE+badCertID; this test asserts that's what
+// ChromeOS sees when it polls.
+func TestSCEPHandler_ChromeOSPKIMessage_GetCertInitial(t *testing.T) {
+	fix := newChromeOSStackFixture(t)
+	pkiMessage := buildChromeOSStylePKIMessage(t, fix, domain.SCEPMessageTypeGetCertInitial, "txn-poll-1", "shared-secret-123", "poll.example.com", aesKeyForOID(pkcs7.OIDAES256CBC))
+
+	w, body := postPKIOperation(t, fix.handler, pkiMessage)
+	if w.Code != http.StatusOK {
+		t.Fatalf("POST PKIOperation (poll): got %d, want 200 (body=%q)", w.Code, body)
+	}
+	if fix.svc.getCertInitialEnvelope == nil {
+		t.Fatal("GetCertInitialWithEnvelope was not called — dispatch missed messageType=20")
+	}
+	// The response should be a CertRep with pkiStatus=2 (FAILURE) +
+	// failInfo=4 (badCertID).
+	certRep, err := pkcs7.ParseSignedData(body)
+	if err != nil {
+		t.Fatalf("ParseSignedData: %v", err)
+	}
+	if len(certRep.SignerInfos) == 0 {
+		t.Fatal("CertRep has no signerInfos")
+	}
+	si := certRep.SignerInfos[0]
+	statusRV, ok := si.AuthAttributes[pkcs7.OIDSCEPPKIStatus.String()]
+	if !ok {
+		t.Fatal("CertRep missing pkiStatus auth-attr")
+	}
+	statusStr := decodeFirstSetMember(t, statusRV)
+	if statusStr != string(domain.SCEPStatusFailure) {
+		t.Errorf("pkiStatus = %q, want %q (FAILURE)", statusStr, domain.SCEPStatusFailure)
+	}
+}
+
+// TestSCEPHandler_ChromeOSPKIMessage_BadPOPO builds a PKIMessage with the
+// signerInfo signature corrupted; expects the handler to fall through to
+// the MVP path (the RFC 8894 verifier rejects the message, and the MVP
+// path also rejects it because the encrypted EnvelopedData isn't a raw
+// CSR). Result: HTTP 400 with a clear error message.
+func TestSCEPHandler_ChromeOSPKIMessage_BadPOPO(t *testing.T) {
+	fix := newChromeOSStackFixture(t)
+	pkiMessage := buildChromeOSStylePKIMessage(t, fix, domain.SCEPMessageTypePKCSReq, "txn-bad-popo", "shared-secret-123", "bad.example.com", aesKeyForOID(pkcs7.OIDAES256CBC))
+	// Tamper with the LAST byte of the message (which lands inside the
+	// signature OCTET STRING for a non-trivial chance of corrupting the
+	// signature without breaking the outer DER framing).
+	pkiMessage[len(pkiMessage)-1] ^= 0xff
+
+	w, _ := postPKIOperation(t, fix.handler, pkiMessage)
+	if w.Code != http.StatusBadRequest && w.Code != http.StatusOK {
+		t.Errorf("POST PKIOperation (bad POPO): got %d, want 400 (MVP fall-through rejection) or 200 (CertRep+failInfo)", w.Code)
+	}
+	if fix.svc.pkcsReqEnvelope != nil {
+		t.Errorf("PKCSReqWithEnvelope was called despite invalid signerInfo signature — POPO check failed open")
+	}
+}
+
+// TestSCEPHandler_ChromeOSPKIMessage_AESVariants exercises AES-128, 192,
+// and 256-CBC. ChromeOS picks based on the GetCACaps response; verify
+// all three round-trip correctly.
+func TestSCEPHandler_ChromeOSPKIMessage_AESVariants(t *testing.T) {
+	cases := []struct {
+		name string
+		oid  asn1.ObjectIdentifier
+	}{
+		{"AES-128-CBC", pkcs7.OIDAES128CBC},
+		{"AES-192-CBC", pkcs7.OIDAES192CBC},
+		{"AES-256-CBC", pkcs7.OIDAES256CBC},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			fix := newChromeOSStackFixture(t)
+			pkiMessage := buildChromeOSStylePKIMessage(t, fix, domain.SCEPMessageTypePKCSReq, "txn-aes-"+tc.name, "shared-secret-123", "aes.example.com", aesKeyForOID(tc.oid))
+			pkiMessage = withContentEncryptionOID(t, pkiMessage, fix, tc.oid, aesKeyForOID(tc.oid))
+			w, body := postPKIOperation(t, fix.handler, pkiMessage)
+			if w.Code != http.StatusOK {
+				t.Fatalf("POST PKIOperation (%s): got %d, want 200 (body=%q)", tc.name, w.Code, body)
+			}
+		})
+	}
+}
+
+// TestSCEPHandler_MVPCompat_StillWorks asserts the existing MVP path (raw
+// CSR inside a stripped SignedData, no EnvelopedData) STILL works for
+// backward compat with lightweight clients.
+func TestSCEPHandler_MVPCompat_StillWorks(t *testing.T) {
+	// Build an MVP-shape request: a SignedData whose encapContent is a
+	// raw CSR (no EnvelopedData wrapper). The legacy handler path
+	// extractCSRFromPKCS7 unwraps it.
+	deviceKey, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		t.Fatalf("rsa.GenerateKey: %v", err)
+	}
+	csrDER := buildTestCSR(t, deviceKey, "mvp.example.com", "mvp-shared-secret")
+
+	// Wrap in MVP-shape PKCS#7 SignedData (encapContent = CSR DER as
+	// OCTET STRING). The existing extractCSRFromPKCS7 handles this.
+	mvpPKCS7 := buildMVPSignedData(t, csrDER)
+
+	svc := &chromeOSMockSCEPService{
+		enrollResult: &domain.SCEPEnrollResult{
+			CertPEM: pemEncodeCert(selfSignedRSACertRaw(t, deviceKey, "mvp-issued.example.com")),
+		},
+	}
+	// Note: NO RA pair set — the handler runs MVP-only.
+	handler := NewSCEPHandler(svc)
+	w, body := postPKIOperation(t, handler, mvpPKCS7)
+	if w.Code != http.StatusOK {
+		t.Fatalf("MVP path POST: got %d, want 200 (body=%q)", w.Code, body)
+	}
+	// Response is the legacy certs-only PKCS#7, NOT a CertRep PKIMessage.
+	if got := w.Header().Get("Content-Type"); got != "application/x-pki-message" {
+		t.Errorf("Content-Type = %q, want application/x-pki-message", got)
+	}
+}
+
+// --- helpers -------------------------------------------------------------
+
+func postPKIOperation(t *testing.T, h SCEPHandler, body []byte) (*httptest.ResponseRecorder, []byte) {
+	t.Helper()
+	req := httptest.NewRequest(http.MethodPost, "/scep?operation=PKIOperation", bytes.NewReader(body))
+	w := httptest.NewRecorder()
+	h.HandleSCEP(w, req)
+	respBody, _ := io.ReadAll(w.Body)
+	return w, respBody
+}
+
+// buildChromeOSStylePKIMessage builds a real SCEP PKIMessage targeting the
+// fixture's RA cert. Mirrors what ChromeOS / micromdm-style clients emit:
+// SignedData(SignerInfo(deviceCert, sig over auth-attrs)) wrapping an
+// EnvelopedData(KTRI(raCert), AES-CBC(CSR + challengePassword)).
+func buildChromeOSStylePKIMessage(t *testing.T, fix *chromeOSStackFixture, messageType domain.SCEPMessageType, transactionID, challengePassword, csrCN string, symKey []byte) []byte {
+	t.Helper()
+
+	// 1. Build the inner CSR carrying the challengePassword attribute.
+	csrDER := buildTestCSR(t, fix.deviceKey, csrCN, challengePassword)
+
+	// 2. Encrypt the CSR via AES-CBC under symKey + random IV.
+	iv := make([]byte, aes.BlockSize)
+	if _, err := rand.Read(iv); err != nil {
+		t.Fatalf("rand iv: %v", err)
+	}
+	ciphertext := aesCBCEncrypt(t, symKey, iv, csrDER)
+
+	// 3. RSA-encrypt the symKey to fix.raCert.PublicKey.
+	encryptedKey, err := rsa.EncryptPKCS1v15(rand.Reader, fix.raCert.PublicKey.(*rsa.PublicKey), symKey)
+	if err != nil {
+		t.Fatalf("rsa encrypt symKey: %v", err)
+	}
+
+	// 4. Build EnvelopedData wrapping ciphertext.
+	envelopedData := buildEnvelopedDataForTest(t, fix.raCert, encryptedKey, iv, ciphertext, oidForAESKeyLen(t, len(symKey)))
+
+	// 5. Build the SignedData carrying the EnvelopedData with a
+	//    signerInfo signed by the device's transient cert/key.
+	signedData := buildSignedDataForTest(t, fix.deviceKey, fix.deviceCert, messageType, transactionID, []byte("0123456789abcdef"), envelopedData)
+	return signedData
+}
+
+// withContentEncryptionOID rewrites the AES OID inside an already-built
+// PKIMessage by re-building from scratch with the new OID. Simpler than
+// surgically patching the bytes.
+func withContentEncryptionOID(t *testing.T, _ []byte, fix *chromeOSStackFixture, oid asn1.ObjectIdentifier, symKey []byte) []byte {
+	t.Helper()
+	csrDER := buildTestCSR(t, fix.deviceKey, "aes.example.com", "shared-secret-123")
+	iv := make([]byte, 16)
+	if _, err := rand.Read(iv); err != nil {
+		t.Fatalf("rand iv: %v", err)
+	}
+	ciphertext := aesCBCEncrypt(t, symKey, iv, csrDER)
+	encryptedKey, err := rsa.EncryptPKCS1v15(rand.Reader, fix.raCert.PublicKey.(*rsa.PublicKey), symKey)
+	if err != nil {
+		t.Fatalf("rsa encrypt: %v", err)
+	}
+	envelopedData := buildEnvelopedDataForTest(t, fix.raCert, encryptedKey, iv, ciphertext, oid)
+	return buildSignedDataForTest(t, fix.deviceKey, fix.deviceCert, domain.SCEPMessageTypePKCSReq, "txn-aes", []byte("0123456789abcdef"), envelopedData)
+}
+
+func aesCBCEncrypt(t *testing.T, key, iv, plaintext []byte) []byte {
+	t.Helper()
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		t.Fatalf("aes.NewCipher: %v", err)
+	}
+	bs := block.BlockSize()
+	padLen := bs - len(plaintext)%bs
+	padded := append([]byte{}, plaintext...)
+	for i := 0; i < padLen; i++ {
+		padded = append(padded, byte(padLen))
+	}
+	enc := cipher.NewCBCEncrypter(block, iv)
+	out := make([]byte, len(padded))
+	enc.CryptBlocks(out, padded)
+	return out
+}
+
+// oidForAESKeyLen maps an AES key length to its CBC OID. Helper for the
+// AES-variants table-driven test.
+func oidForAESKeyLen(t *testing.T, n int) asn1.ObjectIdentifier {
+	t.Helper()
+	switch n {
+	case 16:
+		return pkcs7.OIDAES128CBC
+	case 24:
+		return pkcs7.OIDAES192CBC
+	case 32:
+		return pkcs7.OIDAES256CBC
+	}
+	t.Fatalf("oidForAESKeyLen: unsupported key length %d", n)
+	return nil
+}
+
+// aesKeyForOID returns a deterministic-length symmetric key matching the
+// AES variant identified by oid. Test-only — production uses crypto/rand.
+func aesKeyForOID(oid asn1.ObjectIdentifier) []byte {
+	switch {
+	case oid.Equal(pkcs7.OIDAES128CBC):
+		return bytes.Repeat([]byte{0x42}, 16)
+	case oid.Equal(pkcs7.OIDAES192CBC):
+		return bytes.Repeat([]byte{0x42}, 24)
+	case oid.Equal(pkcs7.OIDAES256CBC):
+		return bytes.Repeat([]byte{0x42}, 32)
+	case oid.Equal(pkcs7.OIDDESEDE3CBC):
+		return bytes.Repeat([]byte{0x42}, 24)
+	}
+	return nil
+}
+
+// buildTestCSR creates a CSR with a challengePassword attribute. Used by
+// the buildChromeOSStylePKIMessage helper to populate the EnvelopedData
+// inner content.
+func buildTestCSR(t *testing.T, key *rsa.PrivateKey, commonName, challengePassword string) []byte {
+	t.Helper()
+	// Build the challengePassword attribute (RFC 2985 §5.4.1, OID
+	// 1.2.840.113549.1.9.7).
+	cpAttr := pkix.AttributeTypeAndValue{
+		Type:  asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 9, 7},
+		Value: challengePassword,
+	}
+	cpAttrSet, err := asn1.Marshal(cpAttr)
+	if err != nil {
+		t.Fatalf("marshal cp attr: %v", err)
+	}
+	tmpl := &x509.CertificateRequest{
+		Subject: pkix.Name{CommonName: commonName},
+		// Inject the challengePassword as a raw extra extension via the
+		// CSR Attributes field.
+		ExtraExtensions: []pkix.Extension{},
+		Attributes: []pkix.AttributeTypeAndValueSET{
+			{
+				Type: asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 9, 7},
+				Value: [][]pkix.AttributeTypeAndValue{
+					{{Type: asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 9, 7}, Value: challengePassword}},
+				},
+			},
+		},
+	}
+	_ = cpAttrSet
+	der, err := x509.CreateCertificateRequest(rand.Reader, tmpl, key)
+	if err != nil {
+		t.Fatalf("CreateCertificateRequest: %v", err)
+	}
+	return der
+}
+
+// buildEnvelopedDataForTest builds an EnvelopedData targeting raCert with
+// a single KTRI carrying the encrypted symmetric key + the AES-CBC
+// ciphertext. Mirrors the Phase 3 buildEnvelopedDataAES256 internal helper
+// but exposed at test scope.
+func buildEnvelopedDataForTest(t *testing.T, raCert *x509.Certificate, encryptedKey, iv, ciphertext []byte, contentEncOID asn1.ObjectIdentifier) []byte {
+	t.Helper()
+	// IssuerAndSerial of the recipient.
+	serialDER, err := asn1.Marshal(raCert.SerialNumber)
+	if err != nil {
+		t.Fatalf("marshal serial: %v", err)
+	}
+	risBody := append([]byte{}, raCert.RawIssuer...)
+	risBody = append(risBody, serialDER...)
+	risBytes := pkcs7.ASN1Wrap(0x30, risBody)
+
+	keyEncAlg := pkix.AlgorithmIdentifier{Algorithm: pkcs7.OIDRSAEncryption, Parameters: asn1.NullRawValue}
+	keyEncAlgBytes, err := asn1.Marshal(keyEncAlg)
+	if err != nil {
+		t.Fatalf("marshal keyEncAlg: %v", err)
+	}
+	encryptedKeyBytes := pkcs7.ASN1Wrap(0x04, encryptedKey)
+
+	ktriBody := append([]byte{}, []byte{0x02, 0x01, 0x00}...)
+	ktriBody = append(ktriBody, risBytes...)
+	ktriBody = append(ktriBody, keyEncAlgBytes...)
+	ktriBody = append(ktriBody, encryptedKeyBytes...)
+	ktriBytes := pkcs7.ASN1Wrap(0x30, ktriBody)
+
+	recipientInfosBytes := pkcs7.ASN1Wrap(0x31, ktriBytes)
+
+	ivOctet := pkcs7.ASN1Wrap(0x04, iv)
+	contentAlg := pkix.AlgorithmIdentifier{
+		Algorithm:  contentEncOID,
+		Parameters: asn1.RawValue{FullBytes: ivOctet},
+	}
+	contentAlgBytes, err := asn1.Marshal(contentAlg)
+	if err != nil {
+		t.Fatalf("marshal contentAlg: %v", err)
+	}
+
+	encContentField := pkcs7.ASN1Wrap(0x80, ciphertext)
+	oidDataBytes := []byte{0x06, 0x09, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x07, 0x01}
+	eciBody := append([]byte{}, oidDataBytes...)
+	eciBody = append(eciBody, contentAlgBytes...)
+	eciBody = append(eciBody, encContentField...)
+	eciBytes := pkcs7.ASN1Wrap(0x30, eciBody)
+
+	envBody := append([]byte{}, []byte{0x02, 0x01, 0x00}...)
+	envBody = append(envBody, recipientInfosBytes...)
+	envBody = append(envBody, eciBytes...)
+	return pkcs7.ASN1Wrap(0x30, envBody)
+}
+
+// buildSignedDataForTest builds a CMS SignedData with the device cert as
+// the signer + auth-attrs carrying SCEP messageType / transactionID /
+// senderNonce + messageDigest of the encapContent.
+func buildSignedDataForTest(t *testing.T, signerKey *rsa.PrivateKey, signerCert *x509.Certificate, messageType domain.SCEPMessageType, transactionID string, senderNonce, encapContent []byte) []byte {
+	t.Helper()
+	contentDigest := sha256.Sum256(encapContent)
+
+	// Auth-attrs SET-OF body.
+	var attrSetBody []byte
+	attrSetBody = append(attrSetBody, attrSeqHelper(t, pkcs7.OIDContentType, pkcs7.ASN1Wrap(0x06, []byte{0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x07, 0x01}))...)
+	attrSetBody = append(attrSetBody, attrSeqHelper(t, pkcs7.OIDMessageDigest, pkcs7.ASN1Wrap(0x04, contentDigest[:]))...)
+	attrSetBody = append(attrSetBody, attrSeqHelper(t, pkcs7.OIDSCEPMessageType, pkcs7.ASN1Wrap(0x13, []byte(intToASCII(int(messageType)))))...)
+	attrSetBody = append(attrSetBody, attrSeqHelper(t, pkcs7.OIDSCEPTransactionID, pkcs7.ASN1Wrap(0x13, []byte(transactionID)))...)
+	attrSetBody = append(attrSetBody, attrSeqHelper(t, pkcs7.OIDSCEPSenderNonce, pkcs7.ASN1Wrap(0x04, senderNonce))...)
+
+	// Sign over SET OF Attribute (RFC 5652 §5.4 quirk).
+	signedAttrsForSig := pkcs7.ASN1Wrap(0x31, attrSetBody)
+	digest := sha256.Sum256(signedAttrsForSig)
+	sig, err := rsa.SignPKCS1v15(rand.Reader, signerKey, 5, digest[:]) // 5 = crypto.SHA256
+	if err != nil {
+		t.Fatalf("sign: %v", err)
+	}
+
+	// SignerInfo SEQUENCE.
+	versionBytes := []byte{0x02, 0x01, 0x01}
+	serialDER, _ := asn1.Marshal(signerCert.SerialNumber)
+	sidBody := append([]byte{}, signerCert.RawIssuer...)
+	sidBody = append(sidBody, serialDER...)
+	sidBytes := pkcs7.ASN1Wrap(0x30, sidBody)
+
+	digestAlg := pkix.AlgorithmIdentifier{Algorithm: pkcs7.OIDSHA256, Parameters: asn1.NullRawValue}
+	digestAlgBytes, _ := asn1.Marshal(digestAlg)
+
+	signedAttrsImplicit := pkcs7.ASN1Wrap(0xa0, attrSetBody)
+
+	sigAlg := pkix.AlgorithmIdentifier{Algorithm: pkcs7.OIDRSAWithSHA256, Parameters: asn1.NullRawValue}
+	sigAlgBytes, _ := asn1.Marshal(sigAlg)
+
+	sigOctet := pkcs7.ASN1Wrap(0x04, sig)
+
+	siBody := append([]byte{}, versionBytes...)
+	siBody = append(siBody, sidBytes...)
+	siBody = append(siBody, digestAlgBytes...)
+	siBody = append(siBody, signedAttrsImplicit...)
+	siBody = append(siBody, sigAlgBytes...)
+	siBody = append(siBody, sigOctet...)
+	siBytes := pkcs7.ASN1Wrap(0x30, siBody)
+
+	// encapContentInfo
+	octetWrap := pkcs7.ASN1Wrap(0x04, encapContent)
+	explicitWrap := pkcs7.ASN1Wrap(0xa0, octetWrap)
+	oidDataBytes := []byte{0x06, 0x09, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x07, 0x01}
+	encapBody := append([]byte{}, oidDataBytes...)
+	encapBody = append(encapBody, explicitWrap...)
+	encapBytes := pkcs7.ASN1Wrap(0x30, encapBody)
+
+	// certificates [0] IMPLICIT SET OF Certificate
+	certsBytes := pkcs7.ASN1Wrap(0xa0, signerCert.Raw)
+
+	// digestAlgorithms SET OF
+	digestAlgsBytes := pkcs7.ASN1Wrap(0x31, digestAlgBytes)
+	// signerInfos SET OF
+	signerInfosBytes := pkcs7.ASN1Wrap(0x31, siBytes)
+
+	// SignedData SEQUENCE
+	sdBody := append([]byte{}, []byte{0x02, 0x01, 0x01}...)
+	sdBody = append(sdBody, digestAlgsBytes...)
+	sdBody = append(sdBody, encapBytes...)
+	sdBody = append(sdBody, certsBytes...)
+	sdBody = append(sdBody, signerInfosBytes...)
+	sdSeq := pkcs7.ASN1Wrap(0x30, sdBody)
+
+	// ContentInfo wrap
+	contentField := pkcs7.ASN1Wrap(0xa0, sdSeq)
+	oidSignedData := []byte{0x06, 0x09, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x07, 0x02}
+	ciBody := append([]byte{}, oidSignedData...)
+	ciBody = append(ciBody, contentField...)
+	return pkcs7.ASN1Wrap(0x30, ciBody)
+}
+
+// buildMVPSignedData builds a degenerate SignedData where the encapContent
+// is the raw CSR bytes — what lightweight SCEP clients send. Used by the
+// MVP-compat test to confirm the legacy parser still works.
+func buildMVPSignedData(t *testing.T, csrDER []byte) []byte {
+	t.Helper()
+	octetWrap := pkcs7.ASN1Wrap(0x04, csrDER)
+	explicitWrap := pkcs7.ASN1Wrap(0xa0, octetWrap)
+	oidDataBytes := []byte{0x06, 0x09, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x07, 0x01}
+	encapBody := append([]byte{}, oidDataBytes...)
+	encapBody = append(encapBody, explicitWrap...)
+	encapBytes := pkcs7.ASN1Wrap(0x30, encapBody)
+
+	digestAlgsBytes := pkcs7.ASN1Wrap(0x31, nil)
+	signerInfosBytes := pkcs7.ASN1Wrap(0x31, nil)
+
+	sdBody := append([]byte{}, []byte{0x02, 0x01, 0x01}...)
+	sdBody = append(sdBody, digestAlgsBytes...)
+	sdBody = append(sdBody, encapBytes...)
+	sdBody = append(sdBody, signerInfosBytes...)
+	sdSeq := pkcs7.ASN1Wrap(0x30, sdBody)
+
+	contentField := pkcs7.ASN1Wrap(0xa0, sdSeq)
+	oidSignedData := []byte{0x06, 0x09, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x07, 0x02}
+	ciBody := append([]byte{}, oidSignedData...)
+	ciBody = append(ciBody, contentField...)
+	return pkcs7.ASN1Wrap(0x30, ciBody)
+}
+
+func attrSeqHelper(t *testing.T, oid asn1.ObjectIdentifier, value []byte) []byte {
+	t.Helper()
+	oidBytes, err := asn1.Marshal(oid)
+	if err != nil {
+		t.Fatalf("marshal OID %v: %v", oid, err)
+	}
+	setOfValue := pkcs7.ASN1Wrap(0x31, value)
+	body := append([]byte{}, oidBytes...)
+	body = append(body, setOfValue...)
+	return pkcs7.ASN1Wrap(0x30, body)
+}
+
+func decodeFirstSetMember(t *testing.T, rv asn1.RawValue) string {
+	t.Helper()
+	var inner asn1.RawValue
+	if _, err := asn1.Unmarshal(rv.Bytes, &inner); err != nil {
+		t.Fatalf("unmarshal SET first member: %v", err)
+	}
+	return string(inner.Bytes)
+}
+
+func intToASCII(i int) string {
+	if i == 0 {
+		return "0"
+	}
+	var b []byte
+	for i > 0 {
+		b = append([]byte{byte('0' + i%10)}, b...)
+		i /= 10
+	}
+	return string(b)
+}
+
+func selfSignedRSACert(t *testing.T, key *rsa.PrivateKey, cn string) *x509.Certificate {
+	t.Helper()
+	der := selfSignedRSACertRaw(t, key, cn)
+	cert, err := x509.ParseCertificate(der)
+	if err != nil {
+		t.Fatalf("ParseCertificate: %v", err)
+	}
+	return cert
+}
+
+func selfSignedRSACertRaw(t *testing.T, key *rsa.PrivateKey, cn string) []byte {
+	t.Helper()
+	tmpl := &x509.Certificate{
+		SerialNumber: big.NewInt(time.Now().UnixNano()),
+		Subject:      pkix.Name{CommonName: cn},
+		Issuer:       pkix.Name{CommonName: cn},
+		NotBefore:    time.Now().Add(-time.Hour),
+		NotAfter:     time.Now().Add(30 * 24 * time.Hour),
+		KeyUsage:     x509.KeyUsageDigitalSignature,
+	}
+	der, err := x509.CreateCertificate(rand.Reader, tmpl, tmpl, &key.PublicKey, key)
+	if err != nil {
+		t.Fatalf("CreateCertificate: %v", err)
+	}
+	return der
+}
+
+func pemEncodeCert(der []byte) string {
+	return string(pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: der}))
+}
+
+// silence unused-import warnings — these packages are referenced inside
+// helpers above; Go's import-pruning is conservative around test-only
+// uses through other test files.
+var (
+	_ = ecdsa.PublicKey{}
+	_ = elliptic.P256
+	_ = des.NewTripleDESCipher
+)

internal/api/handler/scep_handler_test.go

@@ -59,6 +59,22 @@ func (m *mockSCEPService) PKCSReqWithEnvelope(ctx context.Context, csrPEM string
 	}
 }
 
+// RenewalReqWithEnvelope + GetCertInitialWithEnvelope added in Phase 4 to
+// satisfy the extended SCEPService interface. Same MVP-only test fixture
+// rules apply — these stubs mirror PKCSReqWithEnvelope's shape.
+func (m *mockSCEPService) RenewalReqWithEnvelope(ctx context.Context, csrPEM string, challengePassword string, envelope *domain.SCEPRequestEnvelope) *domain.SCEPResponseEnvelope {
+	return m.PKCSReqWithEnvelope(ctx, csrPEM, challengePassword, envelope)
+}
+
+func (m *mockSCEPService) GetCertInitialWithEnvelope(_ context.Context, envelope *domain.SCEPRequestEnvelope) *domain.SCEPResponseEnvelope {
+	return &domain.SCEPResponseEnvelope{
+		Status:         domain.SCEPStatusFailure,
+		FailInfo:       domain.SCEPFailBadCertID,
+		TransactionID:  envelope.TransactionID,
+		RecipientNonce: envelope.SenderNonce,
+	}
+}
+
 func TestSCEP_GetCACaps_Success(t *testing.T) {
 	svc := &mockSCEPService{}
 	h := NewSCEPHandler(svc)

internal/api/router/router_scep_profiles_test.go

@@ -43,14 +43,23 @@ func (s *scepProfileMockService) PKCSReq(_ context.Context, _, _, _ string) (*do
 	return nil, nil
 }
 
-// PKCSReqWithEnvelope was added to the SCEPService interface in SCEP RFC 8894
-// + Intune master bundle Phase 2.4. The router-level tests don't drive the
-// RFC 8894 path; this stub satisfies the interface so the per-profile
+// PKCSReqWithEnvelope / RenewalReqWithEnvelope / GetCertInitialWithEnvelope
+// were added to the SCEPService interface in SCEP RFC 8894 + Intune master
+// bundle Phase 2.4 + Phase 4. The router-level tests don't drive the
+// RFC 8894 path; these stubs satisfy the interface so the per-profile
 // dispatch tests still compile.
 func (s *scepProfileMockService) PKCSReqWithEnvelope(_ context.Context, _, _ string, env *domain.SCEPRequestEnvelope) *domain.SCEPResponseEnvelope {
 	return &domain.SCEPResponseEnvelope{Status: domain.SCEPStatusSuccess, TransactionID: env.TransactionID}
 }
 
+func (s *scepProfileMockService) RenewalReqWithEnvelope(_ context.Context, _, _ string, env *domain.SCEPRequestEnvelope) *domain.SCEPResponseEnvelope {
+	return &domain.SCEPResponseEnvelope{Status: domain.SCEPStatusSuccess, TransactionID: env.TransactionID}
+}
+
+func (s *scepProfileMockService) GetCertInitialWithEnvelope(_ context.Context, env *domain.SCEPRequestEnvelope) *domain.SCEPResponseEnvelope {
+	return &domain.SCEPResponseEnvelope{Status: domain.SCEPStatusFailure, FailInfo: domain.SCEPFailBadCertID, TransactionID: env.TransactionID}
+}
+
 func TestRouter_RegisterSCEPHandlers_LegacyEmptyPathIDMapsToRoot(t *testing.T) {
 	r := New()
 	svc := &scepProfileMockService{tag: "legacy"}