Ruby Rack Middleware

Aserto::Authorization is a middleware that allows Ruby applications to use Aserto as the Authorization provider.

Installation

Add to your application Gemfile:

gem "aserto"

And then execute:

bundle install

Or install it yourself as:

gem install aserto

Configuration

The following configuration settings are required for the authorization middleware:

• policy_id
• tenant_id
• authorizer_api_key
• policy_root

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

The middleware accepts the following optional parameters:

Parameter name	Default value	Description
enabled	true	Enables or disables Aserto Authorization
service_url	"authorizer.prod.aserto.com:8443"	Sets the URL for the authorizer endpoint.
decision	"allowed"	The decision that will be used by the middleware when creating an authorizer request.
logger	STDOUT	The logger to be used by the middleware.
identity_mapping	{ type: :none }	The strategy for retrieveing the identity, possible values: :jwt, :sub, :none
disabled_for	[{}]	Which path and actions to skip the authorization for.
on_unauthorized	-> { return [403, {}, ["Forbidden"]] }	A lambda that is executed when the authorization fails.

Identity

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

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

# configure the middleware 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, the middleware:

• 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, middleware 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

Disable authorization for specific paths

The middleware exposes a disable_for configuration option that accepts an array of hashes with the following keys:

• path - the path to disable authorization for
• actions - an array of actions to disable authorization for

Rails

You can find the paths and actions using bundle exec rails routes

bundle exec rails routes

  Prefix       Verb   URI Pattern               Controller#Action

  api_v1_users GET    /api/users(.:format)      api/v1/users#index {:format=>:json}
               POST   /api/users(.:format)      api/v1/users#create {:format=>:json}
  api_v1_user  GET    /api/users/:id(.:format)  api/v1/users#show {:format=>:json}

# disables get user by id
config.disabled_for = [
  {
    path: '/api/users/:id'
    actions: [:GET]
  }
]

Examples

Rails

# config/initializers/aserto.rb

Rails.application.config.middleware.use Aserto::Authorization 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.prod.aserto.com:8443"
  config.decision = "allowed"
  config.logger = Rails.logger
  config.identity_mapping = {
    type: :sub,
    from: :sub
  }
  config.disabled_for = [
    {
      path: "/api/users",
      actions: %i[GET POST]
    },
    {
      path: "/api/authentication",
      actions: %i[POST]
    }
  ]
  config.on_unauthorized = lambda do |env|
    puts env
    return [403, {}, ["Forbidden"]]
  end
end

Sinatra

# server.rb

# aserto middleware
use Aserto::Authorization do |config|
  config.enabled = true
  config.policy_id = "my-policy-id"
  config.tenant_id = "my-tenant-id"
  config.authorizer_api_key = ENV['authorizer_api_key']
  config.policy_root = "peoplefinder"
  config.service_url = "authorizer.prod.aserto.com:8443"
  config.decision = "allowed"
  config.disabled_for = [
    {
      path: "/api/users/:id",
      actions: %i[GET]
    },
    {
      path: "/",
      actions: %i[GET]
    }
  ]

end