fido: initial tests for Windows WebAuthn API integration

This adds a fake implementation of WinWebAuthnApi along with a scoped
override of WinWebAuthnApi::GetDefault, as well as a test to verify USB
authenticator instantiation depending on API availability and feature
flag state.

Bug: 898718
Change-Id: Iff3a317b4540986775a40fc872754ba0571ae88a
Reviewed-on: https://chromium-review.googlesource.com/c/1316839
Commit-Queue: Martin Kreichgauer <martinkr@chromium.org>
Reviewed-by: Jun Choi <hongjunchoi@chromium.org>
Reviewed-by: Adam Langley <agl@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606254}

device/fido/BUILD.gn

@@ -143,7 +143,6 @@ component("fido") {
   defines = [ "IS_DEVICE_FIDO_IMPL" ]
 
   deps = [
-    ":buildflags",
     "//components/apdu",
     "//components/cbor",
     "//crypto",
@@ -156,6 +155,7 @@ component("fido") {
   ]
 
   public_deps = [
+    ":buildflags",
     "//base",
     "//device/bluetooth",
     "//services/device/public/mojom",
@@ -307,6 +307,8 @@ source_set("test_support") {
     "//device/fido",
     "//mojo/public/cpp/bindings",
     "//services/device/public/mojom",
+    "//services/service_manager/public/cpp",
+    "//services/service_manager/public/mojom",
     "//testing/gmock",
     "//testing/gtest",
   ]
@@ -329,4 +331,11 @@ source_set("test_support") {
       "mac/scoped_touch_id_test_environment.mm",
     ]
   }
+
+  if (is_win && use_win_webauthn_api) {
+    sources += [
+      "win/fake_webauthn_api.cc",
+      "win/fake_webauthn_api.h",
+    ]
+  }
 }

device/fido/fido_request_handler_base.h

@@ -180,6 +180,10 @@ class COMPONENT_EXPORT(DEVICE_FIDO) FidoRequestHandlerBase
     return transport_availability_info_;
   }
 
+  const AuthenticatorMap& AuthenticatorsForTesting() {
+    return active_authenticators_;
+  }
+
  protected:
   // Subclasses implement this method to dispatch their request onto the given
   // FidoAuthenticator. The FidoAuthenticator is owned by this

device/fido/fido_request_handler_unittest.cc

@@ -12,6 +12,7 @@
 #include "base/test/scoped_task_environment.h"
 #include "device/bluetooth/bluetooth_adapter_factory.h"
 #include "device/bluetooth/test/mock_bluetooth_adapter.h"
+#include "device/fido/buildflags.h"
 #include "device/fido/fake_fido_discovery.h"
 #include "device/fido/fido_constants.h"
 #include "device/fido/fido_device.h"
@@ -174,14 +175,18 @@ class FakeFidoAuthenticator : public FidoDeviceAuthenticator {
 
 class FakeFidoRequestHandler : public FidoRequestHandler<std::vector<uint8_t>> {
  public:
-  FakeFidoRequestHandler(const base::flat_set<FidoTransportProtocol>& protocols,
+  FakeFidoRequestHandler(service_manager::Connector* connector,
+                         const base::flat_set<FidoTransportProtocol>& protocols,
                          FakeHandlerCallback callback)
-      : FidoRequestHandler(nullptr /* connector */,
-                           protocols,
-                           std::move(callback)),
+      : FidoRequestHandler(connector, protocols, std::move(callback)),
         weak_factory_(this) {
     Start();
   }
+  FakeFidoRequestHandler(const base::flat_set<FidoTransportProtocol>& protocols,
+                         FakeHandlerCallback callback)
+      : FakeFidoRequestHandler(nullptr /* connector */,
+                               protocols,
+                               std::move(callback)) {}
   ~FakeFidoRequestHandler() override = default;
 
   void DispatchRequest(FidoAuthenticator* authenticator) override {

device/fido/get_assertion_handler_unittest.cc

@@ -7,25 +7,34 @@
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
+#include "base/stl_util.h"
 #include "base/test/scoped_feature_list.h"
 #include "base/test/scoped_task_environment.h"
+#include "build/build_config.h"
 #include "device/base/features.h"
 #include "device/bluetooth/bluetooth_adapter_factory.h"
 #include "device/bluetooth/test/mock_bluetooth_adapter.h"
 #include "device/fido/authenticator_get_assertion_response.h"
+#include "device/fido/buildflags.h"
 #include "device/fido/ctap_get_assertion_request.h"
 #include "device/fido/device_response_converter.h"
 #include "device/fido/fake_fido_discovery.h"
+#include "device/fido/features.h"
 #include "device/fido/fido_constants.h"
 #include "device/fido/fido_parsing_utils.h"
 #include "device/fido/fido_test_data.h"
 #include "device/fido/fido_transport_protocol.h"
 #include "device/fido/get_assertion_request_handler.h"
+#include "device/fido/hid/fake_hid_impl_for_testing.h"
 #include "device/fido/mock_fido_device.h"
 #include "device/fido/test_callback_receiver.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
+#if defined(OS_WIN) && BUILDFLAG(USE_WIN_WEBAUTHN_API)
+#include "device/fido/win/fake_webauthn_api.h"
+#endif
+
 namespace device {
 
 namespace {
@@ -711,4 +720,63 @@ TEST_F(FidoGetAssertionHandlerTest,
             get_assertion_callback().status());
 }
 
+#if defined(OS_WIN) && BUILDFLAG(USE_WIN_WEBAUTHN_API)
+class GetAssertionRequestHandlerWinTest : public ::testing::Test {
+ protected:
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
+  ScopedFakeWinWebAuthnApi scoped_fake_win_webauthn_api_;
+};
+
+// Verify that the request handler instantiates a HID device backed
+// FidoDeviceAuthenticator or a WinNativeCrossPlatformAuthenticator, depending
+// on feature flag and API availability.
+TEST_F(GetAssertionRequestHandlerWinTest, TestWinUsbDiscovery) {
+  enum class DeviceType {
+    kHid,
+    kWinNative,
+  };
+  const struct TestCase {
+    bool enable_win_webauthn_api;
+    bool enable_feature_flag;
+    DeviceType expect_device_type;
+  } test_cases[] = {
+      {false, false, DeviceType::kHid},
+      {false, true, DeviceType::kHid},
+      {true, false, DeviceType::kHid},
+      {true, true, DeviceType::kWinNative},
+  };
+  size_t i = 0;
+  for (const auto& test : test_cases) {
+    SCOPED_TRACE(i++);
+    scoped_fake_win_webauthn_api_.set_available(test.enable_win_webauthn_api);
+    base::test::ScopedFeatureList scoped_feature_list;
+    // Feature is default off (even with API present).
+    if (test.enable_feature_flag)
+      scoped_feature_list.InitAndEnableFeature(kWebAuthUseNativeWinApi);
+
+    TestGetAssertionRequestCallback cb;
+    ScopedFakeHidManager fake_hid_manager_;
+    auto handler = std::make_unique<GetAssertionRequestHandler>(
+        fake_hid_manager_.service_manager_connector(),
+        base::flat_set<FidoTransportProtocol>(
+            {FidoTransportProtocol::kUsbHumanInterfaceDevice}),
+        CtapGetAssertionRequest(test_data::kRelyingPartyId,
+                                test_data::kClientDataJson),
+
+        cb.callback());
+    scoped_task_environment_.RunUntilIdle();
+
+    fake_hid_manager_.AddFidoHidDevice("guid");
+    scoped_task_environment_.RunUntilIdle();
+
+    EXPECT_EQ(1u, handler->AuthenticatorsForTesting().size());
+    // Crudely distinguish authenticator type by FidoAuthenticator::GetId.
+    EXPECT_EQ(test.expect_device_type == DeviceType::kHid
+                  ? "hid:guid"
+                  : "WinNativeCrossPlatformAuthenticator",
+              handler->AuthenticatorsForTesting().begin()->second->GetId());
+  }
+}
+#endif  // defined(OS_WIN) && BUILDFLAG(USE_WIN_WEBAUTHN_API)
+
 }  // namespace device

device/fido/hid/fake_hid_impl_for_testing.cc

@@ -7,6 +7,10 @@
 #include <utility>
 
 #include "device/fido/fido_parsing_utils.h"
+#include "services/device/public/mojom/constants.mojom.h"
+#include "services/device/public/mojom/hid.mojom.h"
+#include "services/service_manager/public/cpp/connector.h"
+#include "services/service_manager/public/mojom/connector.mojom.h"
 
 namespace device {
 
@@ -126,6 +130,20 @@ void FakeHidManager::AddBinding2(device::mojom::HidManagerRequest request) {
   bindings_.AddBinding(this, std::move(request));
 }
 
+void FakeHidManager::AddFidoHidDevice(std::string guid) {
+  auto c_info = device::mojom::HidCollectionInfo::New();
+  c_info->usage = device::mojom::HidUsageAndPage::New(1, 0xf1d0);
+  auto device = device::mojom::HidDeviceInfo::New();
+  device->guid = std::move(guid);
+  device->product_name = "Test Fido Device";
+  device->serial_number = "123FIDO";
+  device->bus_type = device::mojom::HidBusType::kHIDBusTypeUSB;
+  device->collections.push_back(std::move(c_info));
+  device->max_input_report_size = 64;
+  device->max_output_report_size = 64;
+  AddDevice(std::move(device));
+}
+
 void FakeHidManager::GetDevicesAndSetClient(
     device::mojom::HidManagerClientAssociatedPtrInfo client,
     GetDevicesCallback callback) {
@@ -184,4 +202,16 @@ void FakeHidManager::RemoveDevice(const std::string device_guid) {
   devices_.erase(it);
 }
 
+ScopedFakeHidManager::ScopedFakeHidManager() {
+  service_manager::mojom::ConnectorRequest request;
+  connector_ = service_manager::Connector::Create(&request);
+  service_manager::Connector::TestApi test_api(connector_.get());
+  test_api.OverrideBinderForTesting(
+      service_manager::Identity(device::mojom::kServiceName),
+      device::mojom::HidManager::Name_,
+      base::BindRepeating(&FakeHidManager::AddBinding, base::Unretained(this)));
+}
+
+ScopedFakeHidManager::~ScopedFakeHidManager() = default;
+
 }  // namespace device

device/fido/hid/fake_hid_impl_for_testing.h

@@ -20,6 +20,10 @@
 #include "services/device/public/mojom/hid.mojom.h"
 #include "testing/gmock/include/gmock/gmock.h"
 
+namespace service_manager {
+class Connector;
+}
+
 namespace device {
 
 class MockHidConnection : public device::mojom::HidConnection {
@@ -95,6 +99,9 @@ class FakeHidManager : public device::mojom::HidManager {
   FakeHidManager();
   ~FakeHidManager() override;
 
+  // Invoke AddDevice with a device info struct that mirrors a FIDO USB device.
+  void AddFidoHidDevice(std::string guid);
+
   // device::mojom::HidManager implementation:
   void GetDevicesAndSetClient(
       device::mojom::HidManagerClientAssociatedPtrInfo client,
@@ -118,6 +125,23 @@ class FakeHidManager : public device::mojom::HidManager {
   DISALLOW_COPY_AND_ASSIGN(FakeHidManager);
 };
 
+// ScopedFakeHidManager automatically binds itself to the device service for the
+// duration of its lifetime.
+class ScopedFakeHidManager : public FakeHidManager {
+ public:
+  ScopedFakeHidManager();
+  ~ScopedFakeHidManager() override;
+
+  service_manager::Connector* service_manager_connector() {
+    return connector_.get();
+  }
+
+ private:
+  std::unique_ptr<service_manager::Connector> connector_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedFakeHidManager);
+};
+
 }  // namespace device
 
 #endif  // DEVICE_FIDO_HID_FAKE_HID_IMPL_FOR_TESTING_H_

device/fido/hid/fido_hid_discovery_unittest.cc

@@ -25,21 +25,6 @@ using ::testing::_;
 
 namespace {
 
-device::mojom::HidDeviceInfoPtr MakeFidoHidDevice(std::string guid) {
-  auto c_info = device::mojom::HidCollectionInfo::New();
-  c_info->usage = device::mojom::HidUsageAndPage::New(1, 0xf1d0);
-
-  auto u2f_device = device::mojom::HidDeviceInfo::New();
-  u2f_device->guid = std::move(guid);
-  u2f_device->product_name = "Test Fido Device";
-  u2f_device->serial_number = "123FIDO";
-  u2f_device->bus_type = device::mojom::HidBusType::kHIDBusTypeUSB;
-  u2f_device->collections.push_back(std::move(c_info));
-  u2f_device->max_input_report_size = 64;
-  u2f_device->max_output_report_size = 64;
-  return u2f_device;
-}
-
 device::mojom::HidDeviceInfoPtr MakeOtherDevice(std::string guid) {
   auto other_device = device::mojom::HidDeviceInfo::New();
   other_device->guid = std::move(guid);
@@ -56,35 +41,16 @@ MATCHER_P(IdMatches, id, "") {
 }  // namespace
 
 class FidoHidDiscoveryTest : public ::testing::Test {
- public:
-  base::test::ScopedTaskEnvironment& scoped_task_environment() {
-    return scoped_task_environment_;
-  }
-
-  void SetUp() override {
-    fake_hid_manager_ = std::make_unique<FakeHidManager>();
-
-    service_manager::mojom::ConnectorRequest request;
-    connector_ = service_manager::Connector::Create(&request);
-    service_manager::Connector::TestApi test_api(connector_.get());
-    test_api.OverrideBinderForTesting(
-        service_manager::Identity(device::mojom::kServiceName),
-        device::mojom::HidManager::Name_,
-        base::Bind(&FakeHidManager::AddBinding,
-                   base::Unretained(fake_hid_manager_.get())));
-  }
-
  protected:
   base::test::ScopedTaskEnvironment scoped_task_environment_;
-  std::unique_ptr<service_manager::Connector> connector_;
-  std::unique_ptr<FakeHidManager> fake_hid_manager_;
+  ScopedFakeHidManager fake_hid_manager_;
 };
 
 TEST_F(FidoHidDiscoveryTest, TestAddRemoveDevice) {
-  FidoHidDiscovery discovery(connector_.get());
+  FidoHidDiscovery discovery(fake_hid_manager_.service_manager_connector());
   MockFidoDiscoveryObserver observer;
 
-  fake_hid_manager_->AddDevice(MakeFidoHidDevice("known"));
+  fake_hid_manager_.AddFidoHidDevice("known");
 
   EXPECT_CALL(observer, DiscoveryStarted(&discovery, true));
   discovery.set_observer(&observer);
@@ -93,28 +59,28 @@ TEST_F(FidoHidDiscoveryTest, TestAddRemoveDevice) {
   // Devices initially known to the service before discovery started should be
   // reported as KNOWN.
   EXPECT_CALL(observer, AuthenticatorAdded(&discovery, IdMatches("known")));
-  scoped_task_environment().RunUntilIdle();
+  scoped_task_environment_.RunUntilIdle();
 
   // Devices added during the discovery should be reported as ADDED.
   EXPECT_CALL(observer, AuthenticatorAdded(&discovery, IdMatches("added")));
-  fake_hid_manager_->AddDevice(MakeFidoHidDevice("added"));
-  scoped_task_environment().RunUntilIdle();
+  fake_hid_manager_.AddFidoHidDevice("added");
+  scoped_task_environment_.RunUntilIdle();
 
   // Added non-U2F devices should not be reported at all.
   EXPECT_CALL(observer, AuthenticatorAdded(_, _)).Times(0);
-  fake_hid_manager_->AddDevice(MakeOtherDevice("other"));
+  fake_hid_manager_.AddDevice(MakeOtherDevice("other"));
 
   // Removed non-U2F devices should not be reported at all.
   EXPECT_CALL(observer, AuthenticatorRemoved(_, _)).Times(0);
-  fake_hid_manager_->RemoveDevice("other");
-  scoped_task_environment().RunUntilIdle();
+  fake_hid_manager_.RemoveDevice("other");
+  scoped_task_environment_.RunUntilIdle();
 
   // Removed U2F devices should be reported as REMOVED.
   EXPECT_CALL(observer, AuthenticatorRemoved(&discovery, IdMatches("known")));
   EXPECT_CALL(observer, AuthenticatorRemoved(&discovery, IdMatches("added")));
-  fake_hid_manager_->RemoveDevice("known");
-  fake_hid_manager_->RemoveDevice("added");
-  scoped_task_environment().RunUntilIdle();
+  fake_hid_manager_.RemoveDevice("known");
+  fake_hid_manager_.RemoveDevice("added");
+  scoped_task_environment_.RunUntilIdle();
 }
 
 }  // namespace device

device/fido/win/discovery.cc

@@ -18,6 +18,7 @@ WinNativeCrossPlatformAuthenticatorDiscovery::
     ~WinNativeCrossPlatformAuthenticatorDiscovery() = default;
 
 void WinNativeCrossPlatformAuthenticatorDiscovery::Start() {
+  DCHECK(!authenticator_);
   if (!observer()) {
     return;
   }

device/fido/win/discovery.h

@@ -16,7 +16,8 @@ namespace device {
 
 // Instantiates the authenticator subclass for forwarding requests to external
 // authenticators via the Windows WebAuthn API.
-class WinNativeCrossPlatformAuthenticatorDiscovery : public FidoDiscoveryBase {
+class COMPONENT_EXPORT(DEVICE_FIDO) WinNativeCrossPlatformAuthenticatorDiscovery
+    : public FidoDiscoveryBase {
  public:
   WinNativeCrossPlatformAuthenticatorDiscovery(
       WinWebAuthnApi* const win_webauthn_api,

device/fido/win/fake_webauthn_api.cc

@@ -0,0 +1,65 @@
+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "device/fido/win/fake_webauthn_api.h"
+
+#include "base/logging.h"
+
+namespace device {
+
+FakeWinWebAuthnApi::FakeWinWebAuthnApi() = default;
+FakeWinWebAuthnApi::~FakeWinWebAuthnApi() = default;
+
+bool FakeWinWebAuthnApi::IsAvailable() const {
+  return is_available_;
+}
+
+HRESULT FakeWinWebAuthnApi::IsUserVerifyingPlatformAuthenticatorAvailable(
+    BOOL* result) {
+  *result = false;
+  DCHECK(is_available_);
+  return E_NOTIMPL;
+}
+
+HRESULT FakeWinWebAuthnApi::AuthenticatorMakeCredential(
+    HWND h_wnd,
+    const WEBAUTHN_RP_ENTITY_INFORMATION* rp_information,
+    const WEBAUTHN_USER_ENTITY_INFORMATION* user_information,
+    const WEBAUTHN_COSE_CREDENTIAL_PARAMETERS* pub_key_cred_params,
+    const WEBAUTHN_CLIENT_DATA* client_data,
+    const WEBAUTHN_AUTHENTICATOR_MAKE_CREDENTIAL_OPTIONS* options,
+    ScopedCredentialAttestation* credential_attestation) {
+  DCHECK(is_available_);
+  return E_NOTIMPL;
+}
+
+HRESULT FakeWinWebAuthnApi::AuthenticatorGetAssertion(
+    HWND h_wnd,
+    const wchar_t* rp_id_utf16,
+    const WEBAUTHN_CLIENT_DATA* client_data,
+    const WEBAUTHN_AUTHENTICATOR_GET_ASSERTION_OPTIONS* options,
+    ScopedAssertion* assertion) {
+  DCHECK(is_available_);
+  return E_NOTIMPL;
+}
+
+HRESULT FakeWinWebAuthnApi::CancelCurrentOperation(GUID* cancellation_id) {
+  DCHECK(is_available_);
+  return E_NOTIMPL;
+}
+
+const wchar_t* FakeWinWebAuthnApi::GetErrorName(HRESULT hr) {
+  DCHECK(is_available_);
+  return L"not implemented";
+};
+
+ScopedFakeWinWebAuthnApi::ScopedFakeWinWebAuthnApi() : FakeWinWebAuthnApi() {
+  WinWebAuthnApi::SetDefaultForTesting(this);
+}
+
+ScopedFakeWinWebAuthnApi::~ScopedFakeWinWebAuthnApi() {
+  WinWebAuthnApi::ClearDefaultForTesting();
+}
+
+}  // namespace device

device/fido/win/fake_webauthn_api.h

@@ -0,0 +1,58 @@
+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef DEVICE_FIDO_WIN_FAKE_WEBAUTHN_API_H_
+#define DEVICE_FIDO_WIN_FAKE_WEBAUTHN_API_H_
+#include "base/macros.h"
+#include "device/fido/win/webauthn_api.h"
+
+namespace device {
+
+class FakeWinWebAuthnApi : public WinWebAuthnApi {
+ public:
+  FakeWinWebAuthnApi();
+  ~FakeWinWebAuthnApi() override;
+
+  // Inject the return value for WinWebAuthnApi::IsAvailable().
+  void set_available(bool available) { is_available_ = available; }
+
+  // WinWebAuthnApi:
+  bool IsAvailable() const override;
+  // The following methods all return E_NOTIMPL immediately.
+  HRESULT IsUserVerifyingPlatformAuthenticatorAvailable(
+      BOOL* available) override;
+  HRESULT AuthenticatorMakeCredential(
+      HWND h_wnd,
+      const WEBAUTHN_RP_ENTITY_INFORMATION* rp_information,
+      const WEBAUTHN_USER_ENTITY_INFORMATION* user_information,
+      const WEBAUTHN_COSE_CREDENTIAL_PARAMETERS* pub_key_cred_params,
+      const WEBAUTHN_CLIENT_DATA* client_data,
+      const WEBAUTHN_AUTHENTICATOR_MAKE_CREDENTIAL_OPTIONS* options,
+      ScopedCredentialAttestation* credential_attestation) override;
+  HRESULT AuthenticatorGetAssertion(
+      HWND h_wnd,
+      const wchar_t* rp_id_utf16,
+      const WEBAUTHN_CLIENT_DATA* client_data,
+      const WEBAUTHN_AUTHENTICATOR_GET_ASSERTION_OPTIONS* options,
+      ScopedAssertion* assertion) override;
+  HRESULT CancelCurrentOperation(GUID* cancellation_id) override;
+  // Returns L"not implemented".
+  const wchar_t* GetErrorName(HRESULT hr) override;
+
+ private:
+  bool is_available_ = true;
+};
+
+// ScopedFakeWinWebAuthnApi overrides the value returned
+// by WinWebAuthnApi::GetDefault with itself for the duration of its
+// lifetime.
+class ScopedFakeWinWebAuthnApi : public FakeWinWebAuthnApi {
+ public:
+  ScopedFakeWinWebAuthnApi();
+  ~ScopedFakeWinWebAuthnApi() override;
+};
+
+}  // namespace device
+
+#endif  // DEVICE_FIDO_WIN_FAKE_WEBAUTHN_API_H_

device/fido/win/webauthn_api.cc

@@ -116,12 +116,30 @@ class WinWebAuthnApiImpl : public WinWebAuthnApi {
   bool is_bound_ = false;
 };
 
+static WinWebAuthnApi* kDefaultForTesting = nullptr;
+
 // static
 WinWebAuthnApi* WinWebAuthnApi::GetDefault() {
+  if (kDefaultForTesting) {
+    return kDefaultForTesting;
+  }
+
   static base::NoDestructor<WinWebAuthnApiImpl> api;
   return api.get();
 }
 
+// static
+void WinWebAuthnApi::SetDefaultForTesting(WinWebAuthnApi* api) {
+  DCHECK(!kDefaultForTesting);
+  kDefaultForTesting = api;
+}
+
+// static
+void WinWebAuthnApi::ClearDefaultForTesting() {
+  DCHECK(kDefaultForTesting);
+  kDefaultForTesting = nullptr;
+}
+
 WinWebAuthnApi::~WinWebAuthnApi() = default;
 
 }  // namespace device

device/fido/win/webauthn_api.h

@@ -21,9 +21,6 @@ namespace device {
 // Users must check the result of |IsAvailable| on the instance to verify that
 // the native library was loaded successfully before invoking any of the other
 // methods.
-//
-// TODO(martinkr): Add a ScopedFakeWinWebAuthnApi that overrides
-// |GetDefault| for testing.
 class COMPONENT_EXPORT(DEVICE_FIDO) WinWebAuthnApi {
  public:
   // ScopedCredentialAttestation is a scoped deleter for a
@@ -84,6 +81,11 @@ class COMPONENT_EXPORT(DEVICE_FIDO) WinWebAuthnApi {
 
   // See WebAuthNGetErrorName in <webauthn.h>.
   virtual const wchar_t* GetErrorName(HRESULT hr) = 0;
+
+ private:
+  friend class ScopedFakeWinWebAuthnApi;
+  static void SetDefaultForTesting(WinWebAuthnApi* api);
+  static void ClearDefaultForTesting();
 };
 
 }  // namespace device