Maybe/app/controllers/mfa_controller.rb

class MfaController < ApplicationController
  layout :determine_layout
  skip_authentication only: [ :verify, :verify_code ]

  def new
    redirect_to root_path if Current.user.otp_required?
    Current.user.setup_mfa! unless Current.user.otp_secret.present?
  end

  def create
    if Current.user.verify_otp?(params[:code])
      Current.user.enable_mfa!
      @backup_codes = Current.user.otp_backup_codes
      render :backup_codes
    else
      Current.user.disable_mfa!
      redirect_to new_mfa_path, alert: t(".invalid_code")
    end
  end

  def verify
    @user = User.find_by(id: session[:mfa_user_id])

    if @user.nil?
      redirect_to new_session_path
    end
  end

  def verify_code
    @user = User.find_by(id: session[:mfa_user_id])

    if @user&.verify_otp?(params[:code])
      session.delete(:mfa_user_id)
      @session = create_session_for(@user)
      redirect_to root_path
    else
      flash.now[:alert] = t(".invalid_code")
      render :verify, status: :unprocessable_entity
    end
  end

  def disable
    Current.user.disable_mfa!
    redirect_to settings_security_path, notice: t(".success")
  end

  private

    def determine_layout
      if action_name.in?(%w[verify verify_code])
        "auth"
      else
        "settings"
      end
    end
end