payments_controller.rb

def create
  @credit_card = ActiveMerchant::Billing::CreditCard.new(params[:credit_card])
  @billing_address = Address.new(params[:address])
  @payment = @order.payments.create(:credit_card => @credit_card, :address => @billing_address)
  if @payment.success?
    redirect_to complete_order_url(@order)
  elsif @payment.requires_authentication?
    # A view with an iframe from which the user is redirected to the authentication page
    render :action => 'three_d_iframe'
  else
    flash[:notice] = 'Your payment was unsuccessful'
    render :action => 'new', 
  end
end

# the redirect form that loads into the iframe
def three_d_form
  render :layout => false
end

# the action where users are redirected to once they have completed authentication
def three_d_complete
  @response =  @order.complete_three_d_secure(params[:PaRes], params[:MD])
  if @response.success?
      render :action => 'verification_complete', layout => false
  else
    render :action => 'verification_failed', :layout => false
  end
end