authentication.md

description
Practice safe optimism

Authentication

If you're just trying to bootstrap a proof-of-concept application on your local workstation, you don't technically have to worry about giving ActionCable the ability to distinguish between multiple concurrent users. However, the moment you deploy to a host with more than one person accessing your app, you'll find that you're sharing a session and seeing other people's updates. That isn't what most developers have in mind.

Encrypted Session Cookies

You can use your default Rails encrypted cookie-based sessions to isolate your users into their own sessions. This works great even if your application doesn't have a login system.

{% code title="app/controllers/application_controller.rb" %}

class ApplicationController < ActionController::Base
  before_action :set_action_cable_identifier

  private

  def set_action_cable_identifier
    cookies.encrypted[:session_id] = session.id.to_s
  end
end

{% endcode %}

{% code title="app/channels/application_cable/connection.rb" %}

module ApplicationCable
  class Connection < ActionCable::Connection::Base
    identified_by :session_id

    def connect
      self.session_id = cookies.encrypted[:session_id]
    end
  end
end

{% endcode %}

We need to instruct ActionCable to stream updates on a per-session basis:

{% code title="app/channels/optimism_channel.rb" %}

class OptimismChannel < ApplicationCable::Channel
  def subscribed
    stream_for session_id
  end
end

{% endcode %}

Finally, we need to give Optimism the ability to broadcast updates to the correct channel subscription. We will override Optimism's default "OptimismChannel" with a lambda that returns the subscription identifier. You might already have other values in your initializer, or it might not yet exist at all:

{% code title="config/initializers/optimism.rb" %}

Optimism.configure do |config|
  config.channel = ->(context) { OptimismChannel.broadcasting_for(context.session.id) }
end

{% endcode %}

User-based Authentication

Many Rails apps use the current_user convention or more recently, the Current object to provide a global user context. This gives access to the user scope from almost all parts of your application.

{% code title="app/controllers/application_controller.rb " %}

class ApplicationController < ActionController::Base
  before_action :set_action_cable_identifier

  private

  def set_action_cable_identifier
    cookies.encrypted[:user_id] = current_user&.id
  end
end

{% endcode %}

{% code title="app/channels/application_cable/connection.rb " %}

module ApplicationCable
  class Connection < ActionCable::Connection::Base
    identified_by :current_user

    def connect
      user_id = cookies.encrypted[:user_id]
      return reject_unauthorized_connection if user_id.nil?
      user = User.find_by(id: user_id)
      return reject_unauthorized_connection if user.nil?
      self.current_user = user
    end
  end
end

{% endcode %}

We need to instruct ActionCable to stream updates on a per-session basis:

{% code title="app/channels/optimism_channel.rb" %}

class OptimismChannel < ApplicationCable::Channel
  def subscribed
    stream_for current_user
  end
end

{% endcode %}

Finally, we need to give Optimism the ability to broadcast updates to the correct channel subscription. We will override Optimism's default "OptimismChannel" with a lambda that returns the subscription identifier. You might already have other values in your initializer, or it might not yet exist at all:

{% code title="config/initializers/optimism.rb" %}

Optimism.configure do |config|
  config.channel = ->(context) { OptimismChannel.broadcasting_for(context.current_user) }
end

{% endcode %}

Devise-based Authentication

If you're using the versatile Devise authentication library, your configuration is identical to the User-Based Authentication above, except for how ActionCable looks up a user:

{% code title="app/channels/application_cable/connection.rb" %}

module ApplicationCable
  class Connection < ActionCable::Connection::Base
    identified_by :current_user

    def connect
      self.current_user = find_verified_user
    end

    protected

    def find_verified_user
      if current_user = env["warden"].user
        current_user
      else
        reject_unauthorized_connection
      end
    end
  end
end

{% endcode %}