Multiple session store implementation

016_session_store.rb

RedisSessionStore.logger = Rails.logger

session_options = {:expire_after => 1.day, :key_prefix => 'sessions'}
MultiSessionStore.stores[:plain] = [RedisSessionStore, session_options.merge(:key => '_session_id')]
MultiSessionStore.stores[:secure] = [RedisSessionStore, session_options.merge(:key => '_secure_session_id', :secure => ['production', 'staging'].include?(Rails.env))]
MultiSessionStore.default_store = :plain

MultiSessionStore.routes = [
  ['/admin', :secure],
]

Shopify::Application.config.session_store :multi_session_store

multi_session_store.rb

require 'action_dispatch/middleware/session/abstract_store'
require 'active_support/core_ext/class/attribute_accessors'

class MultiSessionStore < ActionDispatch::Session::AbstractStore
  cattr_accessor :stores, :routes, :default_store
  self.stores = {}

  def call(env)
    instance(env).call(env)
  end

  def instance(env)
    match = routes.find { |path, _| env['PATH_INFO'].start_with?(path) }

    store_name = match ? match.last : default_store
    var_name = "@#{store_name}"

    instance_variable_fetch(var_name) do
      klass, args = stores[store_name]

      klass.new(@app, args)
    end
  end

  def instance_variable_fetch(name, &blk)
    instance_variable_get(name) || instance_variable_set(name, blk.call)
  end
end