PlugRailsCookieSessionStore

Rails compatible Plug session store.

This allows you to share session information between Rails and a Plug-based framework like Phoenix.

Note: The information stored in the session cookie is serialized by Rails. Prior to version 4.1, this information was serialized using Ruby's Marshal format. Since Elixir can't (yet!) read Marshal format we have to configure Rails to serialize its cookie information with its Json Serializer.

How to use with Phoenix

Set Rails serialization format to JSON

In an initialer of your Rails project make sure you set the serializer to JSON:

Rails.application.config.action_dispatch.cookies_serializer = :json

Copy/share the encryption information from Rails to Phoenix.

There are 4 things to copy:

secret_key_base
signing_salt
encryption_salt
session_key

The secret_key_base can be found usually in the Rails' secrets.yml file and should be copied to Phoenix's config.exs file. There should already be a key named like that and you should override it.

The other three values can be found somewhere in the initializers directory of your Rails project. Some people don't set the signing_salt and encryption_salt. If you don't find them, set them like so:

Rails.application.config.session_store :cookie_store, key: '_SOMETHING_HERE_session'
Rails.application.config.action_dispatch.encrypted_cookie_salt =  'encryption salt'
Rails.application.config.action_dispatch.encrypted_signed_cookie_salt = 'signing salt'

Configure the Cookie Store in Phoenix.

Edit the endpoint.ex file and add the following:

# ...
plug Plug.Session,
  store: PlugRailsCookieSessionStore,
  key: "_SOMETHING_HERE_session",
  domain: '.myapp.com',
  secure: true,
  signing_salt: "signing salt",
  encrypt: true,
  encryption_salt: "encryption salt",
  key_iterations: 1000,
  key_length: 64,
  key_digest: :sha,
  serializer: Poison
end

That's it!

To test it, set a session value in your Rails application:

session[:foo] = 'bar'

And print it on Phoenix in whatever Controller you want: