prevent choosing ui_only mfa level

app/controllers/multifactor_auths_controller.rb

@@ -26,13 +26,7 @@ def create
 
   def update
     if current_user.otp_verified?(otp_param)
-      if level_param == "disabled"
-        flash[:success] = t("multifactor_auths.destroy.success")
-        current_user.disable_mfa!
-      else
-        flash[:error] = t(".success")
-        current_user.update!(mfa_level: level_param)
-      end
+      handle_new_level_param
     else
       flash[:error] = t("multifactor_auths.incorrect_otp")
     end
@@ -72,4 +66,17 @@ def seed_and_expire
       session.delete(key)
     end
   end
+
+  def handle_new_level_param
+    case level_param
+    when "disabled"
+      flash[:success] = t("multifactor_auths.destroy.success")
+      current_user.disable_mfa!
+    when "ui_only"
+      flash[:error] = t("multifactor_auths.ui_only_warning")
+    else
+      flash[:error] = t(".success")
+      current_user.update!(mfa_level: level_param)
+    end
+  end
 end

app/controllers/settings_controller.rb

@@ -4,5 +4,11 @@ class SettingsController < ApplicationController
 
   def edit
     @user = current_user
+    @mfa_options = [
+      [t(".mfa.level.ui_and_api"), "ui_and_api"],
+      [t(".mfa.level.ui_and_gem_signin"), "ui_and_gem_signin"],
+      [t(".mfa.level.disabled"), "disabled"]
+    ]
+    @mfa_options.insert(2, [t(".mfa.level.ui_only"), "ui_only"]) if @user.mfa_ui_only?
   end
 end

app/views/settings/edit.html.erb

@@ -6,11 +6,10 @@
     <p><%= t(".mfa.enabled_html") %></p>
     <%= form_tag multifactor_auth_path, method: :put, id: "mfa-edit" do %>
       <%= label_tag :level, t(".mfa.level.title"), class: "form__label" %>
-      <%= select_tag :level, options_for_select([
-        [t(".mfa.level.ui_and_api"), "ui_and_api"],
-        [t(".mfa.level.ui_and_gem_signin"), "ui_and_gem_signin"],
-        [t(".mfa.level.ui_only"), "ui_only"],
-        [t(".mfa.level.disabled"), "disabled"]], @user.mfa_level), class: "form__input form__select" %>
+
+
+      <%= select_tag :level, options_for_select(@mfa_options, @user.mfa_level), class: "form__input form__select" %>
+
       <div class="text_field">
         <%= label_tag :otp, "OTP code", class: "form__label" %>
         <%= text_field_tag :otp, "", class: "form__input", autocomplete: :off %>

config/locales/de.yml

@@ -309,6 +309,7 @@ de:
     require_mfa_enabled:
     setup_recommended:
     strong_mfa_level_recommended:
+    ui_only_warning: 
     new:
       title:
       scan_prompt:

config/locales/en.yml

@@ -296,6 +296,7 @@ en:
     require_mfa_enabled: Your multi-factor authentication has not been enabled. You have to enable it first.
     setup_recommended: For protection of your account and your gems, we encourage you to set up multi-factor authentication. Your account will be required to have MFA enabled in the future.
     strong_mfa_level_recommended: For protection of your account and your gems, we encourage you to change your MFA level to "UI and gem signin" or "UI and API". Your account will be required to have MFA enabled on one of these levels in the future.
+    ui_only_warning: Updating multi-factor authentication to "UI Only" is no longer supported. Please use "UI and gem signin" or "UI and API".
     new:
       title: Enabling multi-factor auth
       scan_prompt: Please scan the qr-code with your authenticator app. If you cannot scan the code, add information below into your app manually.

config/locales/es.yml

@@ -326,6 +326,7 @@ es:
       Primero tienes que activarla.
     setup_recommended:
     strong_mfa_level_recommended:
+    ui_only_warning: 
     new:
       title: Activando autenticación de múltiples factores
       scan_prompt: Por favor escanea el código QR con tu aplicación de Autenticación.

config/locales/fr.yml

@@ -320,6 +320,7 @@ fr:
       Vous devez d'abord l'activer.
     setup_recommended:
     strong_mfa_level_recommended:
+    ui_only_warning: 
     new:
       title: Activer l'authentification multifacteur
       scan_prompt: Veuillez scanner le QR code avec votre app d'authentification.

config/locales/ja.yml

@@ -296,6 +296,7 @@ ja:
     require_mfa_enabled:
     setup_recommended:
     strong_mfa_level_recommended:
+    ui_only_warning: 
     new:
       title:
       scan_prompt:

config/locales/nl.yml

@@ -313,6 +313,7 @@ nl:
     require_mfa_enabled:
     setup_recommended:
     strong_mfa_level_recommended:
+    ui_only_warning: 
     new:
       title:
       scan_prompt:

config/locales/pt-BR.yml

@@ -324,6 +324,7 @@ pt-BR:
     require_mfa_enabled:
     setup_recommended:
     strong_mfa_level_recommended:
+    ui_only_warning: 
     new:
       title:
       scan_prompt:

config/locales/zh-CN.yml

@@ -296,6 +296,7 @@ zh-CN:
     require_mfa_enabled: 你的多重要素验证已停用，请先启用。
     setup_recommended:
     strong_mfa_level_recommended:
+    ui_only_warning: 
     new:
       title: 启用多重要素验证
       scan_prompt: 请用你的验证装置扫描 QR-code。如果你没办法扫描，手动输入下面的资料。

config/locales/zh-TW.yml

@@ -297,6 +297,7 @@ zh-TW:
     require_mfa_enabled: 你的多重要素驗證已停用，請先啟用。
     setup_recommended:
     strong_mfa_level_recommended:
+    ui_only_warning: 
     new:
       title: 啟用多重要素驗證
       scan_prompt: 請用你的驗證裝置掃描 QR-code。如果你沒辦法掃描，手動輸入下面的資料。

test/functional/multifactor_auths_controller_test.rb

@@ -75,16 +75,21 @@ class MultifactorAuthsControllerTest < ActionController::TestCase
           end
         end
 
-        context "on updating to ui_only" do
+        context "on updating to ui_only, flash banner is set and mfa level is unchanged" do
           setup do
             @user.mfa_ui_and_api!
             put :update, params: { otp: ROTP::TOTP.new(@user.mfa_seed).now, level: "ui_only" }
           end
 
           should respond_with :redirect
           should redirect_to("the settings page") { edit_settings_path }
-          should "update mfa level to mfa_ui_only now" do
-            assert_predicate @user.reload, :mfa_ui_only?
+          expected = "Updating multi-factor authentication to \"UI Only\" is no longer supported. Please use \"UI and gem signin\" or \"UI and API\"."
+          should "set flash" do
+            assert_equal(expected, flash[:error])
+          end
+
+          should "mfa level should be same as before" do
+            assert_predicate @user.reload, :mfa_ui_and_api?
           end
         end
 

test/integration/settings_test.rb

@@ -153,6 +153,27 @@ def mfa_key
     assert_equal page.current_path, root_path
   end
 
+  test "shows 'ui only' if user's level is ui_only" do
+    sign_in
+    enable_mfa
+    visit edit_settings_path
+
+    assert page.has_selector?("#level > option:nth-child(4)")
+    assert page.has_content? "UI Only"
+  end
+
+  test "does not shows 'ui only' if user's level is not ui_only" do
+    sign_in
+    enable_mfa
+    visit edit_settings_path
+
+    page.fill_in "otp", with: ROTP::TOTP.new(@user.mfa_seed).now
+    change_auth_level "Disabled"
+
+    refute page.has_selector?("#level > option:nth-child(4)")
+    refute page.has_content? "UI Only"
+  end
+
   teardown do
     Capybara.reset_sessions!
     Capybara.use_default_driver