Signing-in user for integration tests via cookie-only session with Rails, Devise, Capybara, and Cuprite

login_helpers.rb

# spec/system/support/login_helpers.rb
# See this blog post for setup guide: https://evilmartians.com/chronicles/system-of-a-test-setting-up-end-to-end-rails-testing

module LoginHelpers
  def login_as(user)
    # Craft session cookie to make request authenticated (to pass even routing constraints)
    # Compilation of these:
    #  - https://dev.to/nejremeslnici/migrating-selenium-system-tests-to-cuprite-42ah#faster-signin-in-tests
    #  - https://turriate.com/articles/2011/feb/how-to-generate-signed-rails-session-cookie
    #  - https://github.com/rails/rails/blob/43e29f0f5d54294ed61c31ddecdf76c2e1a474f7/actionpack/test/dispatch/cookies_test.rb#L350
    request = ActionDispatch::Request.new(Rails.application.env_config)
    cookie_jar = ActionDispatch::Cookies::CookieJar.new(request)
    session_key = Rails.configuration.session_options[:key]
    session_hash = {"session_id" => SecureRandom.hex(16)}
    warden_serializer = Warden::SessionSerializer.new(request.env)
    session_hash[warden_serializer.key_for(:user)] = warden_serializer.user_serialize(user)
    cookie_jar.signed_or_encrypted[session_key] = {value: session_hash}
    page.driver.set_cookie(
      session_key,
      cookie_jar[session_key],
      domain: CAPYBARA_COOKIE_DOMAIN,
      sameSite: :Lax,
      httpOnly: true
    )
  end

  def logout
    page.driver.clear_cookies
  end
end

RSpec.configure do |config|
  config.include LoginHelpers, type: :system

  config.before(:each, type: :system) do |ex|
    login_as public_send(ex.metadata.fetch(:auth)) if ex.metadata[:auth]
  end
end

sample_spec.rb

# spec/system/sample_spec.rb

# Example usage: provide `:auth` option to `it` with a symbol with name of `let` block

require 'system_helper'

RSpec.describe 'Sample spec for logged-in user profile' do
  let(:user) { create(:user) }

  example 'authenticated user can do something', auth: :user do
    # or `login_as(user)` where needed
    home_page.load
  end
end