Rails::SessionCookie

Fast, loosely coupled requests specs for a cookie-authenticated application.

Key goals:

• how to login under any user in request tests quickly
• how to speed up capybara, selenium tests
• how to login under any user in production using rails console

Why

Probably, you might have seen a lot code like this:

# config/initializers/session_store.rb
Rails.application.config.session_store :cookie_store

# authenticating method (maybe Devise or whatever)
session[:current_user_id] = current_user.id

# somewhere in helper for request specs
def login(current_user)
  post '/login', auth_data(current_user)
end

# now every request spec is calling login request
RSpec.describe 'User interface', type: :request do
  let(:user) { create :user }

  before do
    login(user)
  end

  it 'shows private data' do
    get '/dashboard'
  end
end

In a usual user-driven application this tightly couples all request specs, which require authentication, to the login process. If it fails - everything fails. If it's not blazing fast - it slows the whole suite down.

One may move to token-based authentication, especially when having API. That's reasonable and nice. But HTTP is stateless, really we don't need to do several requests, we can think about a session cookie as a token passed in a special header!

You can easily pass headers in tests, the only hard thing is getting the cookie value. Rails may change how a state is serialized into the session cookie. It can be encrypted or not, marshalled (an old story for rails-3 legacy) or JSONed. Long story short: only rails knows how to generate cookie from data.

This gem replaces your usual process of getting session cookie with the simplest rack app utilizing 2 rails middlewares. Rails is modular, that's cool :)

Installation

# Gemfile
gem 'rails-session_cookie', group: :test

Usage in requests specs

# spec_helper.rb
require 'rails/session_cookie'

def login(current_user)
  # depending on Rails version and session configuration this looks like "cookie_store_key=data--digest; path=/; HttpOnly"
  raw_session_cookie = Rails::SessionCookie::App.new(current_user_id: current_user.id).session_cookie

  # note, it's raw, not `<<`
  cookies.merge(raw_session_cookie)
end

# ...everything else the same

Now you can cache raw_session_cookie globally or per-thread depending on current_user_id to get things even faster!

You can also use the raw_session_cookie directly like this:

get "/", {}, { "HTTP_COOKIE" => raw_session_cookie }

Strictly speaking, you may cache Set-Cookie response header from /login URL to achieve same speed (but not coupling ;) However, never saw this in practice, and consider caching of requests in before-phase bad. YMMV.

Advanced usage

If you need more sophisticated logic:

auth_app = proc { |env|
  # do your magic
  env[Rails::SessionCookie::RACK_SESSION].merge!(context)
  [200, {}, []]
}
raw_session_cookie = Rails::SessionCookie::App.new(auth_app).session_cookie

Of course, you can just make use (and reuse!) of as many procs as you wish.

This effectively achieves the effect as this PR#18230, which allows session mutation in a less invasive way in regard to Rails itself ;)

Warden / Devise

Getting session cookie is dead-simple, just get the cookie this way:

raw_session_cookie = Rails::SessionCookie::WardenApp.new(user).session_cookie

Feature tests using Capybara

Get the cookie as described above according to your setup, and assign this way:

Capybara.current_session.driver.browser.set_cookie raw_session_cookie

TODO: Only tested with :rack_test driver!

Login under any devise user in rails production

If you're in production rails console:

Rails::SessionCookie::WardenApp.new(User.last).session_cookie

If you're on remote/developer instance:

# take values from production console:
secret_key_base = Rails.application.env_config['action_dispatch.secret_key_base']
data = User.serialize_into_session(user) # [[user.id], user.encrypted_password[0,29]]
opts = Rails.application.config.session_options

# in remote rails console:
key = "warden.user.user.key" # "warden.user.#{scope}.key"
Rails::SessionCookie::App.new({ key => data }, opts).session_cookie(secret_key_base: secret_key_base)

Then inject the value inside cookies in browser devtools. This another friendly reminder, why you need to keep your SECRET_KEY_BASE secure!

Benchmarks

NOTE: Sometimes devise's sign_in is still faster than SessionCookie (a little though), because Warden uses an ugly hack, in my opinion, to support test-mode authentication.

But, still, in average performance of this gem is not worse if used with user_id->cookie caching Besides, authentication becomes as transparent as possible and should increase readability if you understand HTTP session cookies principles.

$ appraisal rails-5.1-warden rspec -t performance spec/benchmarks/feature_spec.rb
# or just
$ BUNDLE_GEMFILE=gemfiles/rails_6.0_warden.gemfile bundle exec rspec

Speed using capybara in feature test
  correctness of
    SessionCookie
      is correct
    Devise Helpers
      are correct
  against Devise::Test::Helpers
    is obviously slower separately
    is not slower than devise helpers if using cache and executing multiple specs in a suite

Warming up --------------------------------------
devise sign_in
                        70.000  i/100ms
session cookie
                        70.000  i/100ms
session cookie (no cache)
                        62.000  i/100ms
Calculating -------------------------------------
devise sign_in
                        700.554  (± 5.3%) i/s -      3.500k in   5.011356s
session cookie
                        686.868  (± 4.7%) i/s -      3.430k in   5.005542s
session cookie (no cache)
                        611.439  (± 4.9%) i/s -      3.100k in   5.083986s

Comparison:
devise sign_in           :      700.6 i/s
session cookie           :      686.9 i/s - same-ish: difference falls within error
session cookie (no cache):      611.4 i/s - 1.15x  slower

But when it comes with comparison to a simple custom authentication (see spec/support/rails_app.rb), this gem is several times faster! (custom action checks password, hits database, request touches the whole rails middleware stack)

$ appraisal rails-5.1-warden rspec -t performance spec/benchmarks/request_spec.rb

Speed using custom sign-in in request test
  correctness of
    SessionCookie
      is correct
    usual session controller
      is correct
  against custom sign in route
    is faster separately without cache

Warming up --------------------------------------
custom sign in
                         1.000  i/100ms
session cookie
                         1.759k i/100ms
session cookie (no cache)
                       482.000  i/100ms
Calculating -------------------------------------
custom sign in
                         11.219  (± 0.0%) i/s -     57.000  in   5.082143s
session cookie
                         17.573k (± 2.0%) i/s -     87.950k in   5.006754s
session cookie (no cache)
                          4.714k (± 5.0%) i/s -     23.618k in   5.023448s

Comparison:
session cookie           :    17573.4 i/s
session cookie (no cache):     4714.3 i/s - 3.73x  slower
custom sign in           :       11.2 i/s - 1566.44x  slower