Change request environment variables in Rails integration testing

Question

I have written a functional test that changes some of the request object's environment variables to simulate a user has logged in.

require 'test_helper'
class BeesControllerTest < ActionController::TestCase

  # See that the index page gets called correctly.
  def test_get_index

    @request.env['HTTPS'] = "on"
    @request.env['SERVER_NAME'] = "sandbox.example.com"
    @request.env['REMOTE_USER'] = "joeuser" # Authn/Authz done via REMOTE_USER

    get :index
    assert_response :success
    assert_not_nil(assigns(:bees))
    assert_select "title", "Bees and Honey"
  end
end

The functional test works fine.

Now I want to do something similar as part of integration testing. Here is what I tried:

require 'test_helper'
class CreateBeeTest < ActionController::IntegrationTest
  fixtures :bees

  def test_create
    @request.env['HTTPS'] = "on"
    @request.env['SERVER_NAME'] = "sandbox.example.com"
    @request.env['REMOTE_USER'] = "joeuser" # Authn/Authz done via REMOTE_USER

    https?

    get "/"
    assert_response :success
    [... more ...]
  end
end

I get an error complaining that @request is nil. I suspect this has something to do with the session object, but I am not sure how to get it to work.