Rails + Cucumber/Capybara: How to set/retrieve cookies in tests?

Use https://github.com/nruth/show_me_the_cookies which wraps the driver methods. It has methods for getting cookies, deleting cookies, and a method for creating cookies called create_cookie.

So eventually I figured it out after trying a lot of different things.

Given(/^I didn't log out the last time I was on the site$/) do
  user = FactoryGirl.create(:user)
  visit new_user_session_path
  fill_in('user[email]', with: user.email)
  fill_in('user[password]', with: 'test123')
  click_button('Sign in')

  Capybara.current_session.driver.request.cookies.[]('auth_token').should_not be_nil
  auth_token_value = Capybara.current_session.driver.request.cookies.[]('auth_token')
  Capybara.reset_sessions!
  page.driver.browser.set_cookie("auth_token=#{auth_token_value}")
end

When(/^I go to the homepage$/) do
  visit root_path
end

Then(/^I should automatically be logged in$/) do
  page.should have_content("Logout")
end

UPDATE:

Here's what I use in case I'm using Selenium for some of the tests:

if Capybara.current_session.driver.class == Capybara::Selenium::Driver
  auth_token = page.driver.browser.manage.cookie_named('auth_token')[:value]
  page.driver.browser.manage.delete_all_cookies
  page.driver.browser.manage.add_cookie(:name => "auth_token", :value => auth_token)
else
  puts "cookies = #{Capybara.current_session.driver.request.cookies}"
  Capybara.current_session.driver.request.cookies.[]('auth_token').should_not be_nil
  auth_token_value = Capybara.current_session.driver.request.cookies.[]('auth_token')
  Capybara.reset_sessions!
  page.driver.browser.set_cookie("auth_token=#{auth_token_value}")
end