Add e-mail-based sign in challenge for users with disabled 2FA (#14013)

app/controllers/concerns/two_factor_authentication_concern.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+module TwoFactorAuthenticationConcern
+  extend ActiveSupport::Concern
+
+  included do
+    prepend_before_action :authenticate_with_two_factor, if: :two_factor_enabled?, only: [:create]
+  end
+
+  def two_factor_enabled?
+    find_user&.otp_required_for_login?
+  end
+
+  def valid_otp_attempt?(user)
+    user.validate_and_consume_otp!(user_params[:otp_attempt]) ||
+      user.invalidate_otp_backup_code!(user_params[:otp_attempt])
+  rescue OpenSSL::Cipher::CipherError
+    false
+  end
+
+  def authenticate_with_two_factor
+    user = self.resource = find_user
+
+    if user_params[:otp_attempt].present? && session[:attempt_user_id]
+      authenticate_with_two_factor_attempt(user)
+    elsif user.present? && user.external_or_valid_password?(user_params[:password])
+      prompt_for_two_factor(user)
+    end
+  end
+
+  def authenticate_with_two_factor_attempt(user)
+    if valid_otp_attempt?(user)
+      session.delete(:attempt_user_id)
+      remember_me(user)
+      sign_in(user)
+    else
+      flash.now[:alert] = I18n.t('users.invalid_otp_token')
+      prompt_for_two_factor(user)
+    end
+  end
+
+  def prompt_for_two_factor(user)
+    session[:attempt_user_id] = user.id
+    @body_classes = 'lighter'
+    render :two_factor
+  end
+end