Aserto Rails

Aserto authorization library for Ruby and Ruby on Rails.

Built on top of aserto and ruby-authorizer.

Prerequisites

• Ruby 2.7 or newer.
• Rails 6 or newer.
• An Aserto account.

Installation

Add to your application Gemfile:

gem "aserto-rails"

And then execute:

bundle install

Or install it yourself as:

gem install aserto-rails

Configuration

The following configuration settings are required for authorization:

• policy_id
• tenant_id
• authorizer_api_key
• policy_root

These settings can be retrieved from the Policy Settings page of your Aserto account.

Optional parameters:

Parameter name	Default value	Description
service_url	"authorizer.prod.aserto.com:8443"	Sets the URL for the authorizer endpoint.
decision	"allowed"	The decision that will be used when executing an authorizer request.
logger	STDOUT	The logger to be used.
identity_mapping	{ type: :none }	The strategy for retrieveing the identity, possible values: :jwt, :sub, :none

Identity

To determine the identity of the user, the gem can be configured to use a JWT token or a claim using the identity_mapping config.

# configure the gem to use a JWT token form the `my-auth-header` header.
config.identity_mapping = {
  type: :jwt,
  from: "my-auth-header",
}

# configure the gem to use a claim from the JWT token.
# This will decode the JWT token and extract the `sub` field from payload.
config.identity_mapping = {
  type: :sub,
  from: :sub,
}

The whole identity resolution can be overwritten by providing a custom function.

# config/initializers/aserto.rb

# needs to return a hash with the identity having `type` and `identity` keys.
# supported types: `:jwt, :sub, :none`
Aserto.with_identity_mapper do |request|
  {
    type: :sub,
    identity: "my custom identity",
  }
end

URL path to policy mapping

By default, when computing the policy path:

• converts all slashes to dots
• converts any character that is not alpha, digit, dot or underscore to underscore
• converts uppercase characters in the URL path to lowercases

This behavior can be overwritten by providing a custom function:

# config/initializers/aserto.rb

# must return a String
Aserto.with_policy_path_mapper do |policy_root, request|
  method = request.request_method
  path = request.path_info

  "custom: #{policy_root}.#{method}.#{path}"
end

Resource

A resource can be any structured data that the authorization policy uses to evaluate decisions. By default, gem do not include a resource in authorization calls.

This behavior can be overwritten by providing a custom function:

# config/initializers/aserto.rb

# must return a Hash
Aserto.with_resource_mapper do |request|
  { resource:  request.path_info }
end

Examples

# config/initializers/aserto.rb
require "aserto/rails"

Aserto.configure do |config|
  config.enabled = true
  config.policy_id = "my-policy-id"
  config.tenant_id = "my-tenant-id"
  config.authorizer_api_key = Rails.application.credentials.aserto[:authorizer_api_key]
  config.policy_root = "peoplefinder"
  config.service_url = "authorizer.eng.aserto.com:8443"
  config.decision = "allowed"
  config.logger = Rails.logger
  config.identity_mapping = {
    type: :sub,
    from: :sub
  }
end

Controller helpers

The aserto_authorize! method in the controller will raise an exception if the user is not able to perform the given action.

def show
  aserto_authorize!
  @post = Post.find(params[:id])
end

Setting this for every action can be tedious, therefore the aserto_authorize_resource method is provided to automatically authorize all actions in a RESTful style resource controller. It will use a before action to load the resource into an instance variable and authorize it for every action.

class PostsController < ApplicationController
  aserto_authorize_resource
  # aserto_authorize_resource only: %i[show]
  # aserto_authorize_resource except: %i[index]

  def show
    # getting a single post authorized
  end

  def index
    # getting all posts is authorized
  end
end

Check Permissions

The current user's permissions can then be checked using the allowed?, visible? and enabled? methods in views and controllers.

<% if allowed? :get, "/posts/:id", @post %>
  <%= link_to "View", @post %>
<% end %>