From 096c31af75365c2a3ef7c1854d71045d2ce5ec89 Mon Sep 17 00:00:00 2001
From: Matthias Koerber <koerber@google.com>
Date: Mon, 17 Aug 2026 08:22:43 -0700
Subject: [PATCH] Apply TLD+1 matching to SMS OTP

This change ensures that kAutofillRestrictOtpToSameTldPlusOne is respected in OtpManagerImpl before fetching SMS OTPs.

Specifically:
1. OtpFieldDetector::IsOtpForm is made public static so it can be shared.
2. OtpManagerImpl now calls OtpFieldDetector::IsOtpForm in OnFieldTypesDetermined and GetOtpSuggestions before subscribing/fetching.
3. OtpManager::GetOtpSuggestions interface is updated to accept FormStructure so that implementations can check if the form is valid.

TAG=agy
CONV=76fbbabd-2d8a-44db-ad4b-ddfaeda7296e
Fixed: 498725213

Change-Id: I95cc51debaec1f187c51f99911e2a3dc99f46209
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/8232118
Reviewed-by: Jihad Hanna <jihadghanna@google.com>
Commit-Queue: Matthias Körber <koerber@google.com>
Cr-Commit-Position: refs/heads/main@{#1680560}
---
diff --git a/components/autofill/core/browser/foundations/browser_autofill_manager.cc b/components/autofill/core/browser/foundations/browser_autofill_manager.cc
index 6c3524c..5aa0c9f 100644
--- a/components/autofill/core/browser/foundations/browser_autofill_manager.cc
+++ b/components/autofill/core/browser/foundations/browser_autofill_manager.cc
@@ -1420,9 +1420,10 @@
   // still need to offer Autocomplete.
   // TODO(crbug.com/433224307): Consider early returning here when the cache
   // starts storing all forms and fields.
-  AutofillField* autofill_field =
-      FindMutableFormAndField(form.global_id(), field.global_id())
-          .autofill_field;
+  MutableFormAndField form_and_field =
+      FindMutableFormAndField(form.global_id(), field.global_id());
+  FormStructure* form_structure = form_and_field.form_structure;
+  AutofillField* autofill_field = form_and_field.autofill_field;
 
   auto generate_suggestions_and_maybe_show_ui_phase2 = base::BindOnce(
       &BrowserAutofillManager::GenerateSuggestionsAndMaybeShowUIPhase2,
@@ -1432,14 +1433,14 @@
   // `otp_manager_` may not be instantiated on all platforms. If a focused field
   // is not classified, `autofill_field` is null but the field may be filled by
   // autocomplete.
-  if (otp_manager_ && autofill_field &&
+  if (otp_manager_ && form_structure && autofill_field &&
       autofill_field->Type().GetTypes().contains(ONE_TIME_CODE)) {
     if (!client().IsContextSecure()) {
       std::move(generate_suggestions_and_maybe_show_ui_phase2).Run({});
       return;
     }
     otp_manager_->GetOtpSuggestions(
-        field.origin(),
+        *form_structure, field.origin(),
         std::move(generate_suggestions_and_maybe_show_ui_phase2));
     return;
   }
diff --git a/components/autofill/core/browser/integrators/one_time_tokens/mock_otp_manager.h b/components/autofill/core/browser/integrators/one_time_tokens/mock_otp_manager.h
index db1e8b3..b89c03f 100644
--- a/components/autofill/core/browser/integrators/one_time_tokens/mock_otp_manager.h
+++ b/components/autofill/core/browser/integrators/one_time_tokens/mock_otp_manager.h
@@ -21,7 +21,8 @@
 
   MOCK_METHOD(void,
               GetOtpSuggestions,
-              (const url::Origin& origin,
+              (const FormStructure& form,
+               const url::Origin& origin,
                OtpManager::GetOtpSuggestionsCallback callback),
               (override));
 };
diff --git a/components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector.cc b/components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector.cc
index 9e382bb0..42cca74 100644
--- a/components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector.cc
+++ b/components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector.cc
@@ -22,12 +22,7 @@
 
 namespace autofill {
 
-namespace {
-
-// Returns true if the form contains at least one ONE_TIME_CODE field and
-// all ONE_TIME_CODE fields in the form are same-site with the main frame's
-// origin.
-[[nodiscard]] bool IsOtpForm(const FormStructure& form) {
+bool OtpFieldDetector::IsOtpForm(const FormStructure& form) {
   const bool restrict_to_same_tld = base::FeatureList::IsEnabled(
       features::kAutofillRestrictOtpToSameTldPlusOne);
 
@@ -54,17 +49,6 @@
   return has_otp_field;
 }
 
-// Returns true if the `form_id` in `manager` contains at least one ONE_TIME_CODE
-// field and all ONE_TIME_CODE fields in the form are same-site with the main
-// frame's origin.
-[[nodiscard]] bool IsOtpForm(const AutofillManager& manager,
-                             FormGlobalId form_id) {
-  const FormStructure* form_structure = manager.FindCachedFormById(form_id);
-  return form_structure && IsOtpForm(*form_structure);
-}
-
-}  // namespace
-
 OtpFieldDetector::OtpFieldDetector(AutofillClient* client) {
   if (client) {
     autofill_manager_observation_.Observe(client);
@@ -101,7 +85,8 @@
                                               FormGlobalId form,
                                               FieldTypeSource source,
                                               bool small_forms_were_parsed) {
-  if (IsOtpForm(manager, form)) {
+  const FormStructure* form_structure = manager.FindCachedFormById(form);
+  if (form_structure && IsOtpForm(*form_structure)) {
     AddFormAndNotifyIfNecessary(form);
   } else {
     RemoveFormAndNotifyIfNecessary(form);
diff --git a/components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector.h b/components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector.h
index dabc860..5d1f9da 100644
--- a/components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector.h
+++ b/components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector.h
@@ -16,6 +16,7 @@
 namespace autofill {
 
 class AutofillClient;
+class FormStructure;
 
 // Utility class to observe if a WebContents (with all of its frames)
 // - moves from having 0 OTP fields to >0 OTP fields (only focusable fields are
@@ -56,6 +57,12 @@
   // one OTP field.
   bool IsOtpFieldPresent() const;
 
+  // Returns true if the `form` contains at least one focusable `ONE_TIME_CODE`
+  // field. If `kAutofillRestrictOtpToSameTldPlusOne` is enabled, also requires
+  // that all focusable `ONE_TIME_CODE` fields in the `form` are same-site with
+  // the main frame's origin.
+  [[nodiscard]] static bool IsOtpForm(const FormStructure& form);
+
   // AutofillManager::Observer:
 
   // `OnFieldTypesDetermined` informs us incrementally about the discovery of
diff --git a/components/autofill/core/browser/integrators/one_time_tokens/otp_manager.h b/components/autofill/core/browser/integrators/one_time_tokens/otp_manager.h
index 81bae8e..837e5cf 100644
--- a/components/autofill/core/browser/integrators/one_time_tokens/otp_manager.h
+++ b/components/autofill/core/browser/integrators/one_time_tokens/otp_manager.h
@@ -13,6 +13,8 @@
 
 namespace autofill {
 
+class FormStructure;
+
 // The OtpManager helps the BrowserAutofillManager filling OTPs into webforms.
 //
 // One instance per frame, owned by the BrowserAutofillManager.
@@ -35,7 +37,8 @@
   // an OTP arrived. That's bad for cooperative behavior. Instead the callback
   // should return immediately when no OTPs are cached but the Autofill UI
   // should be updated once OTPs arrive.
-  virtual void GetOtpSuggestions(const url::Origin& origin,
+  virtual void GetOtpSuggestions(const FormStructure& form,
+                                 const url::Origin& origin,
                                  GetOtpSuggestionsCallback callback) = 0;
 };
 
diff --git a/components/autofill/core/browser/integrators/one_time_tokens/otp_manager_impl.cc b/components/autofill/core/browser/integrators/one_time_tokens/otp_manager_impl.cc
index 233cdd7..3edf6e2 100644
--- a/components/autofill/core/browser/integrators/one_time_tokens/otp_manager_impl.cc
+++ b/components/autofill/core/browser/integrators/one_time_tokens/otp_manager_impl.cc
@@ -24,6 +24,7 @@
 #include "components/autofill/core/browser/form_structure.h"
 #include "components/autofill/core/browser/foundations/autofill_client.h"
 #include "components/autofill/core/browser/foundations/browser_autofill_manager.h"
+#include "components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector.h"
 #include "components/autofill/core/browser/integrators/one_time_tokens/otp_phish_guard_delegate.h"
 #include "components/autofill/core/browser/logging/log_manager.h"
 #include "components/autofill/core/common/autofill_internals/log_message.h"
@@ -67,8 +68,14 @@
 OtpManagerImpl::~OtpManagerImpl() = default;
 
 void OtpManagerImpl::GetOtpSuggestions(
+    const FormStructure& form,
     const url::Origin& origin,
     OtpManagerImpl::GetOtpSuggestionsCallback callback) {
+  if (!OtpFieldDetector::IsOtpForm(form)) {
+    std::move(callback).Run({});
+    return;
+  }
+
   // TODO(crbug.com/415273270) This is just a hack to prepopulate the OTPs in
   // case no real backend is triggered. The feature definition should migrate to
   // autofill.
@@ -124,11 +131,7 @@
     return;
   }
 
-  const bool form_contains_otp_field = std::ranges::any_of(
-      form->fields(), [](const std::unique_ptr<AutofillField>& field) {
-        return field->Type().GetTypes().contains(ONE_TIME_CODE);
-      });
-  if (!form_contains_otp_field) {
+  if (!OtpFieldDetector::IsOtpForm(*form)) {
     return;
   }
 
diff --git a/components/autofill/core/browser/integrators/one_time_tokens/otp_manager_impl.h b/components/autofill/core/browser/integrators/one_time_tokens/otp_manager_impl.h
index 9bba6f4..65a092f 100644
--- a/components/autofill/core/browser/integrators/one_time_tokens/otp_manager_impl.h
+++ b/components/autofill/core/browser/integrators/one_time_tokens/otp_manager_impl.h
@@ -28,6 +28,7 @@
 namespace autofill {
 
 class BrowserAutofillManager;
+class FormStructure;
 class LogBuffer;
 
 // Used for histograms. Do not reorder.
@@ -60,7 +61,8 @@
   // OtpManager:
   // Returns any cached OTPs (if they exist) and renews a subscription so that
   // incoming OTPs can be reported.
-  void GetOtpSuggestions(const url::Origin& origin,
+  void GetOtpSuggestions(const FormStructure& form,
+                         const url::Origin& origin,
                          GetOtpSuggestionsCallback callback) override;
 
   // AutofillManager::Observer:
diff --git a/components/autofill/core/browser/suggestions/one_time_passwords/otp_suggestion_generator.cc b/components/autofill/core/browser/suggestions/one_time_passwords/otp_suggestion_generator.cc
index 8126d934..0f9c0f4 100644
--- a/components/autofill/core/browser/suggestions/one_time_passwords/otp_suggestion_generator.cc
+++ b/components/autofill/core/browser/suggestions/one_time_passwords/otp_suggestion_generator.cc
@@ -86,7 +86,7 @@
   }
 
   otp_manager_->GetOtpSuggestions(
-      trigger_field.origin(),
+      *form_structure, trigger_field.origin(),
       base::BindOnce(&OtpSuggestionGenerator::OnOtpReturned,
                      weak_ptr_factory_.GetWeakPtr(), std::move(callback)));
 }
diff --git a/components/autofill/core/browser/foundations/browser_autofill_manager_unittest.cc b/components/autofill/core/browser/foundations/browser_autofill_manager_unittest.cc
index 35885d10..e2f9f85 100644
--- a/components/autofill/core/browser/foundations/browser_autofill_manager_unittest.cc
+++ b/components/autofill/core/browser/foundations/browser_autofill_manager_unittest.cc
@@ -7157,7 +7157,7 @@
   // suggests that.
   const std::vector<std::string> otp_values = {"123456"};
   EXPECT_CALL(otp_manager(), GetOtpSuggestions)
-      .WillOnce(RunOnceCallback<1>(otp_values));
+      .WillOnce(RunOnceCallback<2>(otp_values));
   OnAskForValuesToFill(form, form.fields()[0]);
   EXPECT_TRUE(external_delegate()->on_suggestions_returned_seen());
 
diff --git a/components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector_unittest.cc b/components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector_unittest.cc
index df8b675b..6032d06 100644
--- a/components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector_unittest.cc
+++ b/components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector_unittest.cc
@@ -11,6 +11,8 @@
 #include "base/test/mock_callback.h"
 #include "base/test/scoped_feature_list.h"
 #include "base/test/task_environment.h"
+#include "components/autofill/core/browser/autofill_type.h"
+#include "components/autofill/core/browser/form_structure.h"
 #include "components/autofill/core/browser/foundations/autofill_manager_test_api.h"
 #include "components/autofill/core/browser/foundations/browser_autofill_manager.h"
 #include "components/autofill/core/browser/foundations/test_autofill_client.h"
@@ -421,4 +423,135 @@
                          OtpFieldDetectorAutofillManagerObserverTest,
                          testing::Bool());
 
+namespace {
+
+// Helper to construct a FormStructure with a single field for testing
+// `IsOtpForm`.
+std::unique_ptr<FormStructure> CreateFormWithField(
+    const url::Origin& main_frame_origin,
+    const url::Origin& field_origin,
+    FieldType type,
+    bool is_focusable = true) {
+  FormData form;
+  form.set_main_frame_origin(main_frame_origin);
+  FormFieldData field;
+  field.set_origin(field_origin);
+  field.set_is_focusable(is_focusable);
+  form.set_fields({field});
+
+  auto form_structure = std::make_unique<FormStructure>(form);
+  if (form_structure->fields().empty()) {
+    return nullptr;
+  }
+  form_structure->field(0)->SetTypeTo(AutofillType(type), std::nullopt);
+  return form_structure;
+}
+
+}  // namespace
+
+// Tests that `IsOtpForm` returns false when there are no OTP fields in the
+// form.
+TEST(OtpFieldDetectorIsOtpFormTest, NoOtpField) {
+  std::unique_ptr<FormStructure> form_structure = CreateFormWithField(
+      /*main_frame_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*field_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*type=*/UNKNOWN_TYPE);
+  ASSERT_TRUE(form_structure);
+  EXPECT_FALSE(OtpFieldDetector::IsOtpForm(*form_structure));
+}
+
+// Tests that `IsOtpForm` returns false when the only OTP field is not
+// focusable.
+TEST(OtpFieldDetectorIsOtpFormTest, UnfocusableOtpField) {
+  std::unique_ptr<FormStructure> form_structure = CreateFormWithField(
+      /*main_frame_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*field_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*type=*/ONE_TIME_CODE, /*is_focusable=*/false);
+  ASSERT_TRUE(form_structure);
+  EXPECT_FALSE(OtpFieldDetector::IsOtpForm(*form_structure));
+}
+
+// Tests that `IsOtpForm` returns true when there is a focusable OTP field on
+// the same origin as the main frame.
+TEST(OtpFieldDetectorIsOtpFormTest, FocusableOtpFieldSameOrigin) {
+  std::unique_ptr<FormStructure> form_structure = CreateFormWithField(
+      /*main_frame_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*field_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*type=*/ONE_TIME_CODE, /*is_focusable=*/true);
+  ASSERT_TRUE(form_structure);
+  EXPECT_TRUE(OtpFieldDetector::IsOtpForm(*form_structure));
+}
+
+// Tests that `IsOtpForm` returns true when an OTP field is in a subdomain
+// iframe matching the main frame's TLD+1.
+TEST(OtpFieldDetectorIsOtpFormTest, SameTldPlusOneSubdomain) {
+  base::test::ScopedFeatureList feature_list;
+  feature_list.InitAndEnableFeature(
+      features::kAutofillRestrictOtpToSameTldPlusOne);
+
+  std::unique_ptr<FormStructure> form_structure = CreateFormWithField(
+      /*main_frame_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*field_origin=*/url::Origin::Create(GURL("https://sub.example.com")),
+      /*type=*/ONE_TIME_CODE);
+  ASSERT_TRUE(form_structure);
+  EXPECT_TRUE(OtpFieldDetector::IsOtpForm(*form_structure));
+}
+
+// Tests that `IsOtpForm` returns false when
+// `kAutofillRestrictOtpToSameTldPlusOne` is enabled and an OTP field is in a
+// cross-origin iframe with mismatched TLD+1.
+TEST(OtpFieldDetectorIsOtpFormTest, MismatchedTldPlusOneFeatureEnabled) {
+  base::test::ScopedFeatureList feature_list;
+  feature_list.InitAndEnableFeature(
+      features::kAutofillRestrictOtpToSameTldPlusOne);
+
+  std::unique_ptr<FormStructure> form_structure = CreateFormWithField(
+      /*main_frame_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*field_origin=*/url::Origin::Create(GURL("https://attacker.com")),
+      /*type=*/ONE_TIME_CODE);
+  ASSERT_TRUE(form_structure);
+  EXPECT_FALSE(OtpFieldDetector::IsOtpForm(*form_structure));
+}
+
+// Tests that `IsOtpForm` returns true when
+// `kAutofillRestrictOtpToSameTldPlusOne` is disabled even if an OTP field is in
+// a cross-origin iframe.
+TEST(OtpFieldDetectorIsOtpFormTest, MismatchedTldPlusOneFeatureDisabled) {
+  base::test::ScopedFeatureList feature_list;
+  feature_list.InitAndDisableFeature(
+      features::kAutofillRestrictOtpToSameTldPlusOne);
+
+  std::unique_ptr<FormStructure> form_structure = CreateFormWithField(
+      /*main_frame_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*field_origin=*/url::Origin::Create(GURL("https://attacker.com")),
+      /*type=*/ONE_TIME_CODE);
+  ASSERT_TRUE(form_structure);
+  EXPECT_TRUE(OtpFieldDetector::IsOtpForm(*form_structure));
+}
+
+// Tests that `IsOtpForm` returns false when multiple OTP fields are present and
+// at least one has a mismatched TLD+1 with the main frame.
+TEST(OtpFieldDetectorIsOtpFormTest, MultipleOtpFieldsOneMismatched) {
+  base::test::ScopedFeatureList feature_list;
+  feature_list.InitAndEnableFeature(
+      features::kAutofillRestrictOtpToSameTldPlusOne);
+
+  FormData form;
+  form.set_main_frame_origin(url::Origin::Create(GURL("https://example.com")));
+  FormFieldData field1;
+  field1.set_origin(url::Origin::Create(GURL("https://example.com")));
+  field1.set_is_focusable(true);
+  FormFieldData field2;
+  field2.set_origin(url::Origin::Create(GURL("https://attacker.com")));
+  field2.set_is_focusable(true);
+  form.set_fields({field1, field2});
+
+  FormStructure form_structure(form);
+  ASSERT_EQ(form_structure.fields().size(), 2u);
+  form_structure.field(0)->SetTypeTo(AutofillType(ONE_TIME_CODE), std::nullopt);
+  form_structure.field(1)->SetTypeTo(AutofillType(ONE_TIME_CODE), std::nullopt);
+
+  EXPECT_FALSE(OtpFieldDetector::IsOtpForm(form_structure));
+}
... (file diff truncated)

diff --git a/components/autofill/core/browser/foundations/browser_autofill_manager_unittest.cc b/components/autofill/core/browser/foundations/browser_autofill_manager_unittest.cc
index 35885d10..e2f9f85 100644
--- a/components/autofill/core/browser/foundations/browser_autofill_manager_unittest.cc
+++ b/components/autofill/core/browser/foundations/browser_autofill_manager_unittest.cc
@@ -7157,7 +7157,7 @@
   // suggests that.
   const std::vector<std::string> otp_values = {"123456"};
   EXPECT_CALL(otp_manager(), GetOtpSuggestions)
-      .WillOnce(RunOnceCallback<1>(otp_values));
+      .WillOnce(RunOnceCallback<2>(otp_values));
   OnAskForValuesToFill(form, form.fields()[0]);
   EXPECT_TRUE(external_delegate()->on_suggestions_returned_seen());
diff --git a/components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector_unittest.cc b/components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector_unittest.cc
index df8b675b..6032d06 100644
--- a/components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector_unittest.cc
+++ b/components/autofill/core/browser/integrators/one_time_tokens/otp_field_detector_unittest.cc
@@ -11,6 +11,8 @@
 #include "base/test/mock_callback.h"
 #include "base/test/scoped_feature_list.h"
 #include "base/test/task_environment.h"
+#include "components/autofill/core/browser/autofill_type.h"
+#include "components/autofill/core/browser/form_structure.h"
 #include "components/autofill/core/browser/foundations/autofill_manager_test_api.h"
 #include "components/autofill/core/browser/foundations/browser_autofill_manager.h"
 #include "components/autofill/core/browser/foundations/test_autofill_client.h"
@@ -421,4 +423,135 @@
                          OtpFieldDetectorAutofillManagerObserverTest,
                          testing::Bool());
 
+namespace {
+
+// Helper to construct a FormStructure with a single field for testing
+// `IsOtpForm`.
+std::unique_ptr<FormStructure> CreateFormWithField(
+    const url::Origin& main_frame_origin,
+    const url::Origin& field_origin,
+    FieldType type,
+    bool is_focusable = true) {
+  FormData form;
+  form.set_main_frame_origin(main_frame_origin);
+  FormFieldData field;
+  field.set_origin(field_origin);
+  field.set_is_focusable(is_focusable);
+  form.set_fields({field});
+
+  auto form_structure = std::make_unique<FormStructure>(form);
+  if (form_structure->fields().empty()) {
+    return nullptr;
+  }
+  form_structure->field(0)->SetTypeTo(AutofillType(type), std::nullopt);
+  return form_structure;
+}
+
+}  // namespace
+
+// Tests that `IsOtpForm` returns false when there are no OTP fields in the
+// form.
+TEST(OtpFieldDetectorIsOtpFormTest, NoOtpField) {
+  std::unique_ptr<FormStructure> form_structure = CreateFormWithField(
+      /*main_frame_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*field_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*type=*/UNKNOWN_TYPE);
+  ASSERT_TRUE(form_structure);
+  EXPECT_FALSE(OtpFieldDetector::IsOtpForm(*form_structure));
+}
+
+// Tests that `IsOtpForm` returns false when the only OTP field is not
+// focusable.
+TEST(OtpFieldDetectorIsOtpFormTest, UnfocusableOtpField) {
+  std::unique_ptr<FormStructure> form_structure = CreateFormWithField(
+      /*main_frame_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*field_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*type=*/ONE_TIME_CODE, /*is_focusable=*/false);
+  ASSERT_TRUE(form_structure);
+  EXPECT_FALSE(OtpFieldDetector::IsOtpForm(*form_structure));
+}
+
+// Tests that `IsOtpForm` returns true when there is a focusable OTP field on
+// the same origin as the main frame.
+TEST(OtpFieldDetectorIsOtpFormTest, FocusableOtpFieldSameOrigin) {
+  std::unique_ptr<FormStructure> form_structure = CreateFormWithField(
+      /*main_frame_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*field_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*type=*/ONE_TIME_CODE, /*is_focusable=*/true);
+  ASSERT_TRUE(form_structure);
+  EXPECT_TRUE(OtpFieldDetector::IsOtpForm(*form_structure));
+}
+
+// Tests that `IsOtpForm` returns true when an OTP field is in a subdomain
+// iframe matching the main frame's TLD+1.
+TEST(OtpFieldDetectorIsOtpFormTest, SameTldPlusOneSubdomain) {
+  base::test::ScopedFeatureList feature_list;
+  feature_list.InitAndEnableFeature(
+      features::kAutofillRestrictOtpToSameTldPlusOne);
+
+  std::unique_ptr<FormStructure> form_structure = CreateFormWithField(
+      /*main_frame_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*field_origin=*/url::Origin::Create(GURL("https://sub.example.com")),
+      /*type=*/ONE_TIME_CODE);
+  ASSERT_TRUE(form_structure);
+  EXPECT_TRUE(OtpFieldDetector::IsOtpForm(*form_structure));
+}
+
+// Tests that `IsOtpForm` returns false when
+// `kAutofillRestrictOtpToSameTldPlusOne` is enabled and an OTP field is in a
+// cross-origin iframe with mismatched TLD+1.
+TEST(OtpFieldDetectorIsOtpFormTest, MismatchedTldPlusOneFeatureEnabled) {
+  base::test::ScopedFeatureList feature_list;
+  feature_list.InitAndEnableFeature(
+      features::kAutofillRestrictOtpToSameTldPlusOne);
+
+  std::unique_ptr<FormStructure> form_structure = CreateFormWithField(
+      /*main_frame_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*field_origin=*/url::Origin::Create(GURL("https://attacker.com")),
+      /*type=*/ONE_TIME_CODE);
+  ASSERT_TRUE(form_structure);
+  EXPECT_FALSE(OtpFieldDetector::IsOtpForm(*form_structure));
+}
+
+// Tests that `IsOtpForm` returns true when
+// `kAutofillRestrictOtpToSameTldPlusOne` is disabled even if an OTP field is in
+// a cross-origin iframe.
+TEST(OtpFieldDetectorIsOtpFormTest, MismatchedTldPlusOneFeatureDisabled) {
+  base::test::ScopedFeatureList feature_list;
+  feature_list.InitAndDisableFeature(
+      features::kAutofillRestrictOtpToSameTldPlusOne);
+
+  std::unique_ptr<FormStructure> form_structure = CreateFormWithField(
+      /*main_frame_origin=*/url::Origin::Create(GURL("https://example.com")),
+      /*field_origin=*/url::Origin::Create(GURL("https://attacker.com")),
+      /*type=*/ONE_TIME_CODE);
+  ASSERT_TRUE(form_structure);
+  EXPECT_TRUE(OtpFieldDetector::IsOtpForm(*form_structure));
+}
+
+// Tests that `IsOtpForm` returns false when multiple OTP fields are present and
+// at least one has a mismatched TLD+1 with the main frame.
+TEST(OtpFieldDetectorIsOtpFormTest, MultipleOtpFieldsOneMismatched) {
+  base::test::ScopedFeatureList feature_list;
+  feature_list.InitAndEnableFeature(
+      features::kAutofillRestrictOtpToSameTldPlusOne);
+
+  FormData form;
+  form.set_main_frame_origin(url::Origin::Create(GURL("https://example.com")));
+  FormFieldData field1;
+  field1.set_origin(url::Origin::Create(GURL("https://example.com")));
+  field1.set_is_focusable(true);
+  FormFieldData field2;
+  field2.set_origin(url::Origin::Create(GURL("https://attacker.com")));
+  field2.set_is_focusable(true);
+  form.set_fields({field1, field2});
+
+  FormStructure form_structure(form);
+  ASSERT_EQ(form_structure.fields().size(), 2u);
+  form_structure.field(0)->SetTypeTo(AutofillType(ONE_TIME_CODE), std::nullopt);
+  form_structure.field(1)->SetTypeTo(AutofillType(ONE_TIME_CODE), std::nullopt);
+
+  EXPECT_FALSE(OtpFieldDetector::IsOtpForm(form_structure));
+}
+
 }  // namespace autofill
diff --git a/components/autofill/core/browser/integrators/one_time_tokens/otp_manager_impl_unittest.cc b/components/autofill/core/browser/integrators/one_time_tokens/otp_manager_impl_unittest.cc
index b9279d7..ffe9d18 100644
--- a/components/autofill/core/browser/integrators/one_time_tokens/otp_manager_impl_unittest.cc
+++ b/components/autofill/core/browser/integrators/one_time_tokens/otp_manager_impl_unittest.cc
@@ -6,6 +6,7 @@
 
 #include "base/test/gmock_callback_support.h"
 #include "base/test/metrics/histogram_tester.h"
+#include "base/test/scoped_feature_list.h"
 #include "base/test/task_environment.h"
 #include "base/test/test_future.h"
 #include "base/time/clock.h"
@@ -17,6 +18,7 @@
 #include "components/autofill/core/browser/foundations/with_test_autofill_client_driver_manager.h"
 #include "components/autofill/core/browser/integrators/one_time_tokens/otp_manager_impl_test_api.h"
 #include "components/autofill/core/browser/test_utils/autofill_form_test_utils.h"
+#include "components/autofill/core/common/autofill_features.h"
 #include "components/autofill/core/common/autofill_test_utils.h"
 #include "components/autofill/core/common/form_data.h"
 #include "components/one_time_tokens/core/browser/one_time_token.h"
@@ -26,11 +28,12 @@
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-using autofill::test::FormDescription;
-using autofill::test::GetServerTypes;
-using base::test::RunOnceCallback;
-using one_time_tokens::OneTimeTokenServiceImpl;
-using ::testing::_;
+using ::autofill::test::FormDescription;
+using ::autofill::test::GetServerTypes;
+using ::base::test::RunOnceCallback;
+using ::one_time_tokens::OneTimeTokenServiceImpl;
+using ::testing::Test;
+
 namespace autofill {
 
 namespace {
@@ -67,7 +70,7 @@
 
 }  // namespace
 
-class OtpManagerImplTest : public testing::Test,
+class OtpManagerImplTest : public Test,
                            public WithTestAutofillClientDriverManager<> {
  public:
   OtpManagerImplTest() : one_time_token_service_(&sms_otp_backend_, nullptr) {}
@@ -85,8 +88,9 @@
     test_field_.set_origin(url::Origin::Create(GURL("https://example.test")));
   }
 
-  void AddForm(const FormDescription& form_description) {
+  const FormStructure* AddForm(const FormDescription& form_description) {
     FormData form = test::GetFormData(form_description);
+    FormGlobalId form_id = form.global_id();
     auto form_structure = std::make_unique<FormStructure>(form);
     test_api(*form_structure).SetFieldTypes(GetServerTypes(form_description));
     test_api(*form_structure).AssignSections();
@@ -97,26 +101,36 @@
     // This would typically happen during parsing but is skipped if a form is
     // injected via the test API.
     autofill_manager().NotifyObservers(
-        &TestBrowserAutofillManager::Observer::OnFieldTypesDetermined,
-        form.global_id(),
+        &TestBrowserAutofillManager::Observer::OnFieldTypesDetermined, form_id,
         TestBrowserAutofillManager::Observer::FieldTypeSource::kAutofillAiModel,
         /*small_forms_were_parsed=*/false);
+    return autofill_manager().FindCachedFormById(form_id);
   }
 
-  void AddFormWithOtpField() {
+  const FormStructure* AddFormWithOtpField(
+      std::optional<url::Origin> field_origin = std::nullopt,
+      std::optional<url::Origin> main_frame_origin = std::nullopt,
+      bool is_focusable = true) {
     FormDescription form_description = {
-        .fields = {
-            {.server_type = ONE_TIME_CODE, .label = u"OTP", .name = u"otp"},
-        }};
-    AddForm(form_description);
+        .fields =
+            {
+                {.server_type = ONE_TIME_CODE,
+                 .is_focusable = is_focusable,
+                 .label = u"OTP",
+                 .name = u"otp",
+                 .origin = field_origin},
+            },
+        .main_frame_origin = main_frame_origin,
+    };
+    return AddForm(form_description);
   }
 
-  void AddFormWithFirstNameField() {
+  const FormStructure* AddFormWithFirstNameField() {
     FormDescription form_description = {
         .fields = {
             {.server_type = NAME_FIRST, .label = u"First name", .name = u"fn"},
         }};
-    AddForm(form_description);
+    return AddForm(form_description);
   }
 
   MockOtpPhishGuardDelegate& otp_phish_guard_delegate() {
@@ -169,10 +183,12 @@
       .WillOnce(RunOnceCallback<2>(false));
 
   // Observing an OTP field is supposed to trigger an SMS OTP request.
-  AddFormWithOtpField();
+  const FormStructure* form = AddFormWithOtpField();
+  ASSERT_TRUE(form);
 
   base::test::TestFuture<const std::vector<std::string>> future;
-  otp_manager.GetOtpSuggestions(test_field_.origin(), future.GetCallback());
+  otp_manager.GetOtpSuggestions(*form, test_field_.origin(),
+                                future.GetCallback());
 
   ASSERT_EQ(future.Get().size(), 1u);
   EXPECT_EQ(future.Get()[0], otp.value());
@@ -200,10 +216,12 @@
       .WillOnce(RunOnceCallback<2>(false));
 
   // Observing an OTP field is supposed to trigger an SMS OTP request.
-  AddFormWithOtpField();
+  const FormStructure* form = AddFormWithOtpField();
+  ASSERT_TRUE(form);
 
   base::test::TestFuture<const std::vector<std::string>> future;
-  otp_manager.GetOtpSuggestions(test_field_.origin(), future.GetCallback());
+  otp_manager.GetOtpSuggestions(*form, test_field_.origin(),
+                                future.GetCallback());
 
   // The future should not be ready yet, as the SMS backend has not responded.
   EXPECT_FALSE(future.IsReady());
@@ -231,21 +249,25 @@
       .WillOnce(RunOnceCallback<2>(false));
 
   // Observing an OTP field is supposed to trigger an SMS OTP request.
-  AddFormWithOtpField();
... (truncated)