Set CookieStore key on a request basis

custom_cookie_store.rb

# Set a different cookie key for subdomains so IE will work properly with
# session as in other browsers where cookies are only shared among the exact
# same host name by default.
# 
# e.g. visiting lol-ie.domain.com after visiting domain.com on IE will fetch
# the session / cookie from domain.com instead of fetching the one from lol-ie.domain.com
# 
class CustomCookieStore < ActionDispatch::Session::CookieStore
  def call(env)
    hostname = env['HTTP_HOST'].split(':').first

    @key = "_ss_#{hostname.split('.').first}"
    super(env)
  end
end

Rails.application.config.session_store(:custom_cookie_store, expire_after: 24.hours)