Simple Auth

SimpleAuth is an authentication library to be used when everything else is just too complicated.

This library only handles session. You have to implement the authentication strategy as you want (e.g. in-site authentication, OAuth, etc).

Just the following line to your Gemfile:

gem "simple_auth"

Then run rails generate simple_auth:install to copy the initializer file.

The initializer will install the required helper methods on your controller. So, let's say you want to support user and admin authentication. You'll need to specify the following scope.

# config/initializers/simple_auth.rb
SimpleAuth.setup do |config|
  config.scopes = %i[user admin]
  config.login_url = proc { login_path }
  config.logged_url = proc { dashboard_path }
  config.flash_message_key = :alert

  config.install_helpers!
end

Session is valid only when Controller#authorized_#{scope}? method returns true, which is the default behavior. You can override these methods with your own rules; the following example shows how you can authorize all e-mails from @example.com to access the admin dashboard.

class Admin::DashboardController < ApplicationController
  private
  def authorized_admin?
    current_user.email.match(/@example.com\z/)
  end
end

So, how do you set up a new user session? That's really simple, actually.

class SessionsController < ApplicationController
  def new
  end

  def create
    @user = User.find_by_email(params[:email])

    if @user.try(:authenticate, params[:password])
      SimpleAuth::Session.create(scope: "user", session: session, record: @user)
      redirect_to return_to(dashboard_path)
    else
      flash[:alert] = "Invalid username or password"
      render :new
    end
  end

  def destroy
    reset_session
    redirect_to root_path
  end
end

First thing to notice is that SimpleAuth doesn't care about how you authenticate. You could easily set up a different authentication strategy, e.g. API tokens. The important part is assigning the record: and scope: options. The return_to helper will give you the requested url (before the user logged in) or the default url.

SimpleAuth uses GlobalID as the session identifier. This allows using any objects that respond to #to_gid, including namespaced models and POROs.

session[:user_id]
#=> gid://myapp/User/1

If you need to locate a record using such value, you can do it by calling GlobalID::Locator.locate(session[:user_id])

Finally, only ActiveRecord::RecordNotFound errors are trapped by SimpleAuth (when ActiveRecord is available). If you locator raises a different exception, add the error class to the list of known exceptions.

SimpleAuth::Session.record_not_found_exceptions << CustomNotFoundRecordError

Logging out a user is just as simple; all you have to do is calling the regular reset_session.

You can restrict access by using 2 macros. Use redirect_logged_#{scope} to avoid rendering a page for logged user.

class SignupController < ApplicationController
  before_action :redirect_logged_user
end

Use require_logged_#{scope} to enforce authenticated access.

class DashboardController < ApplicationController
  before_action :require_logged_user
end

"So which helpers are defined?", you ask. Just three simple helpers.

#{scope}_logged_in?    # e.g. user_logged_in? (available in controller & views)
current_#{scope}       # e.g. current_user    (available in controller & views)
#{scope}_session       # e.g. user_session    (available in controller & views)

You can also restrict routes directly from your routes:

Rails.application.routes.draw do
  authenticate :admin, ->(user) { user.admin? } do
    mount Sidekiq::Web, at: "sidekiq"
  end
end

In this case, :admin is the scope and the lambda will only be called whenever there's a valid record associated with that record.

simple_auth supports ActionController::API-based controllers. Include the SimpleAuth::ActionController::API module in your API controller:

class ApiController < ActionController::API
  include SimpleAuth::ActionController::API

  before_action :authenticate_via_token
  before_action :require_logged_user

  def index
    render json: {message: "hello there"}
  end

  private def authenticate_via_token
    user = User.find_by_api_token(id: request.headers["Authorization"])

    return render(plain: "401 Unauthorized", status: :unauthorized) unless user

    SimpleAuth::Session.create(scope: "user", session:, record: user)
  end
end

By default, unauthorized requests receive a 401 Unauthorized plain text response. You can override render_unauthorized_access(authorization) to customize this behavior. The authorization object gives you access to authorization.error_message, which contains the translated error message for the failed authorization:

class ApiController < ActionController::API
  include SimpleAuth::ActionController::API

  private def render_unauthorized_access(authorization)
    render json: {error: authorization.error_message}, status: :unauthorized
  end
end

These are the translations you'll need:

---
en:
  simple_auth:
    user:
      unlogged_in: "You need to be logged in"
      unauthorized: "You don't have permission to access this page"

If you don't set these translations, a default message will be used.

To display the error message, use something like <%= flash[:alert] %>. If you want to use a custom key, say :error, use the configuration file config/initializers/simple_auth.rb to define the new key:

# config/initializers/simple_auth.rb
SimpleAuth.setup do |config|
  # ...

  config.flash_message_key = :error

  # ...
end

• Nando Vieira

• https://github.com/fnando/simple_auth/contributors

For more details about how to contribute, please read https://github.com/fnando/simple_auth/blob/main/CONTRIBUTING.md.

The gem is available as open source under the terms of the MIT License. A copy of the license can be found at https://github.com/fnando/simple_auth/blob/main/LICENSE.md.

Everyone interacting in the simple_auth project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.