Authz is an opinionated almost-turnkey solution for managing authorization in your Rails application.

Authz provides you with:

• An authorization admin interface that allows non-developers to configure how authorization works for your app without changing any code. The admin makes it very easy to redefine what a role can do and to answer questions like "who can create reports"? or "what can John Doe do?"
• An opinionated approach to structure your authorization rules that promotes clarity and maintainability.
• An easy-to-use API that allows developers to integrate Authz into their apps with very little code, while providing them with all the tools they need.
  • "Can I make my views dynamic depending on the user's authorization?" Yup!
  • "Can I retrieve only the records the user has access to?" Sure thing!
  • "The role structure inside my organization changes frequently and I spend a lot of time updating the 'who-can-do-what' code to keep up with the changes.'" No worries. Use the admin to make the tweaks you need, no code changes.

Get Started with our Video Tutorial Series and follow along with the live demo.

We will be adding new videos to the series as we produce them. Anything not covered in the videos can be found in this README.

• Quick Start
• Is Authz A Good Match For My Needs?
• Requirements
• Installation and Initial Setup
• Usage
  • How Authorization Rules Work in Authz
    • Permissions
    • Scoping Rules
  • Usage for Authorization Admins
    • Cold-start Configuration
    • Business as Usual
    • Maintenance
  • Usage for Developers
    • Scopables
    • Controllers
      • authorize
      • apply_authz_scopes
    • Views
      • authorized_path?
      • authz_link_to
    • Programmatic Interaction with Authz
• Performance and Caching
  • In-request caching
  • Cross-request caching
  • Fragment and Russian Doll caching
• Common Problems and Solutions
• License

Authz was built for applications that need a particular type of authorization which is very common and relatively simple. However, there are many other types of authorization rules that are out of the scope of this gem. The following questions will help you assess if Authz is a good match for you.

1. Are you expecting to use Authz to authorize other applications other than the application you installed it in? (e.g. Using it as an authorization service for another app)

   • Yes: Sorry, Authz was built to provide authorization for its host app only.
   • No: Good match!

2. Do you need to grant authorization considering factors other than the action that is being performed and the instance/resource it is being performed on?

   • For example:
     • Users must be denied access after 10 pm.
     • Users must be granted access based on their IP address.
     • Customers must be denied access when the transaction amount is greater than $5000.
   • Yes. If these types of rules are not very common in your app, you may still benefit from Authz provided that you take care of these cases yourself. If they are common, you are better off checking out other projects like Pundit or CanCanCan.
   • No: Good match!

3. Here are some examples of rules that can be configured in Authz. Do they look compatible with your needs?

   • Examples:
     • The general director role must be able to index/show/new/create/... the reports from all cities and all departments.
     • The regional director role must be able to index/show/new/create/... the reports from their city and all departments.
     • The regional auditor role must only be able to index/show the reports from their city and all departments.
     • The writer role must be able to index/show/new/create/... the reports from their city and their department.
     • John Doe can simultaneously be a regional auditor in San Francisco and a writer in New York for the 'Sports' department.
   • Yes: Good Match!
   • No: Sorry, Authz was built to support rules that involve actions being performed on resources. Roles are authorized to perform those actions on a certain subest of those resources, like the reports that belong to New York and the Sports Department.

Back to table of content

• Rails >= 5.0 using ActiveRecord on a relational database.
• Your app already has an authentication mechanism like Devise.
• Optional: Your preference of caching technology through ActiveSupport::Cache.

Add this line to your application's Gemfile:

gem 'authz'

And then execute in your terminal:

$ bundle install

Then install Authz executing:

$ rails g authz:install
# => config/initializer/authz.rb gets created
# => The authz migrations are installed
$ rails db:migrate

Seed Authz's tables with the data required to control access to the Authorization Admin. This will create a Business Process in the Authz::BusinessProcesses table. Any role that is granted that business process will get full access to the Authorization Admin.

• Later, you will also probably want to run this in production to configure it. See Cold Start Configuration for more details.

$ rails authz:seed_admin

Go to config/initializer/authz.rb and configure:

unless Rails.configuration.eager_load
  # The scopables location
  Dir[Rails.root.join('app/scopables/**/*.rb')].each{ |f| require f }
end
Authz.configure do |config|
  # The method that Authz should use to force authentication into the Authorization Admin
  config.force_authentication_method = :authenticate_user!
  # The method used to access the current user
  config.current_user_method = :current_user
  # ...
  # config.cross_request_caching = true 
end

Go to config/routes.rb and mount the Authz engine admin on the path of your choice:

Rails.application.routes.draw do
  mount Authz::Engine => '/authz', as: 'authz'
  # ...
end

Go to app/models/ and open the model that manages your authenticated users (typically the User class) and:

• include the Authz::Models::Rolable module which indicates Authz that users can be granted roles (see Usage for more info).
• Use the authz_label_method to define which method should Authz use to label each user inside the admin.

class User < ApplicationRecord
  include Authz::Models::Rolable 
  authz_label_method :email
  # ...
end

Go to app/controllers/application_controller.rb and:

• include Authz::Controllers::AuthorizationManager. This will make all controllers that inherit from the ApplicationController capable of performing authorization. Alternatively, you may include this only in the controllers that you want.
• Optional: Authz will raise a ::NotAuthorized exception whenever a user attempts to perform a forbidden action. You may want to rescue_from it and define how to handle it gracefully. The admin will also use this handler when unauthorized access is attempted, but only if placed inside the ApplicationController.
• Optional: As a safeguard you can declare an around_action :verify_authorized which will raise an ::AuthorizationNotPerformedError exception if a developer forgets to authorize a controller action or to explicitly skip_authorization (see Usage for more info). Alternatively, you may also do this inside each controller individually (particularly if you are using devise).

class ApplicationController < ActionController::Base
  before_action :authenticate_user! # Typical for devise
  include Authz::Controllers::AuthorizationManager
  rescue_from Authz::Controllers::AuthorizationManager::NotAuthorized, with: :unauthorized_handler
  # around_action :verify_authorized # Optional
  
  #... 

  private
  # Note that the redirect uses main_app.(something).
  # main_app is must be used to avoid ambiguity between
  # your app and the engines you use if there are route helpers 
  # with the same name (like root_url)  
  def unauthorized_handler
    msg = 'Ooops! It seems that you are not authorized to do that!'
    respond_to do |format|
      format.html { redirect_back fallback_location: main_app.root_url, alert: msg }
      format.js{ render(js: "alert('#{msg}');") }
    end
  end
end

You are done with installation. The next step is to learn how authorization rules work in Authz. If you already know this, go to the Scopables section.

Back to table of content

This library has 2 types of users and therefore there is a usage section for each:

• Authorization admins (non-developers), who will manage the system once it is deployed.
• Developers, in charge of integrating the library into their application.

Before jumping into the details for each user type, it is very important that both developers and admins understand how authorization rules are organised in Authz.

In Authz users are granted one or many roles. Roles determine what a user is authorized to do, for example, John may only edit blog post #1 if he has been granted at least one role that is authorized to do so. As a consequence, a user with no roles cannot do anything.

A role has permission to perform some actions on a certain scope (set) of instances. Permissions and Scoping Rules are the core components to determine if an action over a resource is authorized. The next figure illustrates this with an example.

Lets dive a little deeper into Permissions and Scoping Rules.

Back to table of content

Permissions is the term we use to denote what a role can do. Permissions are actually organised in a hierarchical structure designed to make the system intuitive and maintainable.

At the most fine-grained level we find the ControllerActions. Simply put, a ControllerAction is an action that can be performed over a resource class; for example Reports#update indicates the action of updating resources of class Report.

ControllerActions are a common thing in the developer world so don't worry, your developers will help you set-up this part.

ControllerActions are grouped into BusinessProcesses, each reflecting a real-life process that your business has. For example, a newspaper might have "publish reports" and "write reports" processes, each requiring a different set of controller actions to get the job done.

Roles are granted the power to execute one or many BusinessProcesses. The next figure illustrates this with an example.

We strongly recommend thinking about your authorization needs in terms of actions, business processes and roles as this structure is easy to explain to other non-technical stakeholders. However, you are more than welcome to bend this suggestion and use the BusinessProcesses and Roles as mere groupings in any way it makes sense for your business.

Back to table of content

Permissions only define what a given role can do over certain resource classes. ScopingRules determine on which entities those permissions can be applied. This is better explained through an example.

Lets imagine that our multi-city newspaper application needs to implement the following authorization rules:

• As a "New York Sports Editor" I need to be able to perform the "publish report" and "moderate comments" business processes only for the Sports department and for New York.
• As a "San Fran Sports Editor" ... same as above... only for the Sports department and for San Francisco.
• As a "Director" I need to be able to perform all business processes for all cities and for all departments.

The application for this newspaper needs multiple models to work: the Cities where it operates, the Departments in which the business is internally divided, the Reports they produce, the Readersthat have paid for a subscription, the Comments the readers leave on the reports, etc. However, despite all these models, only the information about the City and the Department is relevant to the authorization rules.

We call these classes Scoping Classes as they define the scope of the permissions granted to a role. For the case of the "New York Sports Editor" role, the permissions to "publish reports" and to "moderate comments" are scoped down to Reports and Comments that belong to "New York" City and the "Sports" Department. In Authz terminology, we say that a “New York Sports Editor” is authorized to do any of his granted permissions only on resources that are within his scope, which is defined by his configured Scoping Rules:

• ScopableByCity = 'New York
• ScopableByDepartment = Sports

The next figure illustrates how everything fits together.

Note to developers: if you are thinking "NY Sports Editor and SF Sports Editor, that looks like a unnecessary repetition..." take a look at the Scopables section. It is simple to DRY this up, it's just easier to explain the concepts this way.

These Scoping Classes typically exists inside the application's domain logic or are easy enough to implement and fit nicely into the domain. If you can't express your authorization rules in terms of Scoping Classes then Authz is probably not for you.

Back to table of content

Authz comes with a built-in authorization GUI from which admins can configure everything related to authorization. The GUI can be accessed through a URL/path configured by the developers.

There are 3 types of activities that admins do through the GUI: cold-start configuration, business as usual and maintenance.

Cold-start makes reference to configuring all the permissions, scoping rules and roles on a brand new Authz installation.

For teams that are integrating Authz into an existing live project we recommend doing the cold-start configuration using a rake task, since they probably can’t afford to have all users locked out while the admin manually configures everything through the GUI. More information on how to do this on: Programmatic Interaction with Authz.

Teams can also opt to use the GUI to manually configure everything. Authz uses itself to authorize the access to the GUI, so the “first ever” admin needs to be granted permission to access the GUI by a developer through the console. Authz provides a the rails authz:seed_admin rake task to automatically seed everything needed to access the GUI (more information on the Installation Section).

Back to table of content

During “business as usual” an admin will make changes to the authorization configuration to keep up with the business’ needs, like granting, creating and revoking roles.

The GUI provides the admins full control of the authorization system without requiring any code modifications and re-deployments. Through the GUI admins can:

• Create, view, update and delete controller actions, business processes, scoping rules and roles.
• Grant and revoke roles to users.

The admin also makes it very easy to answer questions like “who can cancel orders?” or “what can John do?”.

Back to table of content

The authorization configuration will need maintenance as developers make changes to the codebase. In particular, maintenance is needed when developers add/remove controller actions from the application or add/remove/change the scopables or keywords for the scoping rules.

The GUI’s main dashboard detects differences from the current in-database configuration and the codebase, and suggests the adjustments that need to be done. However, nothing replaces good communication between the developers and the authorization admins.

Back to table of content

The authorization logic bits inside your app typically live in 3 places: Scopables, Controllers and Views. You may also interact with the Authz models directly.

This is the first thing to do if you have just installed the gem.

Start by identifying which are the Scoping Classes inside your app that you need to meet your authorization needs. For the rest of this section we will carry on with our newspaper example where the scoping classes are City and Department.

A Scopable is a plain old ruby module that extends from Authz::Scopables::Base. Scopables are used to indicate to Authz which keywords are available for the configuration of ScopingRules and what do they mean.

Given that City is a scoping class, we need to create a ScopableByCity module (note the naming convention) that must define two methods:

• .available_keywords must return an array of strings with the available keywords for scoping by city.
• .resolve_keyword must translate the given keyword into an array of the ids of the cities that are available for that keyword. The method must take 2 arguments: keyword and requester (the instance of the user that is being authorized).
  • If you add +[nil] to the array of ids resolved, you allow the bearer of the keyword to have access to resources that are NOT associated with any city, like reports or comments with no city.
• You can use the special keyword 'All', which will give the bearer access to all cities. You don't need to resolve All in your #resolve_keyword method.

We recommend creating an app/scopables directory to place the scopables, but you can put them wherever you want. Just remember to adjust the authz.rb initializer accordingly.

module ScopableByCity
  extend Authz::Scopables::Base
  
  # It must return an array of strings
  def self.available_keywords
    # You can query the DB to generate the available keywords
    City.all.pluck(:name) + ['All']
    
    # ... or you can define some custom keywords that make sense for your needs
    %w[high-altitude low-altitude]
    
    # ... many applications allow some users to access only resources "they own"
    # e.g. access to "my cities"
    %w[mine All]
  end
  
  # It must return an array if ids
  def self.resolve_keyword(keyword, requester)
    # If your keyword is an attribute, you can resolve it like this  
    City.where('LOWER(name) IS ?', keyword.downcase).pluck(:id) + [nil]
   
    # ... Or if it is something else
    if keyword == 'high-altitude'
     City.get_high_altitude.pluck(:id)
    elsif keyword == 'low-altitude'
      City.get_low_altitude.pluck(:id)
    end 
    
    # ... You can even use the requester to resolve using anything in your domain
    if keyword == 'mine'
      requester.cities.pluck(:id) 
    end
  end

end

The next step is to indicate to Authz which models of your app need to be scoped by city for authorization purposes. For example, if we want to grant or deny authorization for Reports based on the city scoping rule, we must include the ScopableByCity in the Report class.

• The Report class must have an active record association to City. It can be any type of association, including through: :other_model.
• Authz will use automatically look for associations based on the name of the Scopable (:city and :cities in this case). If your association name is different or if you have both :city and :cities associations, indicate the name of the association to use using #set_scopable_by_city_association_name.

class Report < ApplicationRecord
  belongs_to :city
  include ScopableByCity
  # set_scopable_by_city_association_name :ciudad
end

You might want to determine access to instances of a class based on more than one ScopingRule. For example, for reports we want to grant access only if the requester has the correct City and Department.

This is very easy to achieve. Create a ScopableByDepartment module and include it in the Report class.

class Report < ApplicationRecord
  belongs_to :city
  belongs_to :department
  include ScopableByCity
  include ScopableByDepartment
end

The scoping classes like City and Department are trivially scopable by themselves. For example, only users with access to the City instance 'New York' will be able to perform actions on it (like update it).

class City < ApplicationRecord
  # No association needed of course...
  include ScopableByCity 
end

Note that for a given role, the defined scoping rules apply equally on all models. For example, given that the 'ny sports editor' role has a City scoping rule of 'New York' and a Department scoping rule of 'Sports' these rules will apply whenever a 'ny sports editor' is trying to act upon a Report or Comment. If for some reason, when dealing with Reports you want to apply the 'New York' keyword and when dealing with Comments you want to apply the 'San Francisco" keyword, you need to define 2 different roles (they probably are 2 different roles).

Back to table of content

The authorize method is used to perform authorization on a controller action. You must supply the instance on which the action is trying to be executed using the using: @report argument.

class ReportsController < ApplicationController
  #...
  def show
    @report = Report.find(params[:id])
    authorize using: @report
    # Will raise Authz::Controllers::AuthorizationManager::NotAuthorized
    # if not authorized 
  end
end

Authz will check if the current user has any role that allows him to perform the action Reports#show on the instance @report taking into account the role's Scoping Rules. Note that the controller and action name are automatically inferred.

For some actions, we really don't have a sensible instance to use for authorization. In these cases we can use the skip_scoping: true argument to perform authorization based on the permitted actions only.

class ReportsController < ApplicationController
  #...
  def new
     authorize skip_scoping: true
     @report = Report.new
  end
end

For the most part, we can keep the traditional RESTful controller action coding style and just include authorize. Notable exceptions are actions that attempt to #update or #create an instance since we want to make sure that the instance is within the scoping rules after it has been saved. For example, a 'ny sports writer' should not be able to update the city of a 'New York' report to 'San Francisco'.

In simple cases we don't have to do much as Rails handles this through in memory association proxies:

• #create actions keep their RESTful style.
• In #update actions we can use .assign_attributes to change the instance in memory and authz will verify it with the new information.

def create
    @report = Report.new(report_params)
    @report.user = current_user
    authorize using: @report

    if @report.save
      redirect_to @report, notice: 'Report was successfully created.'
    else
      render :new
    end
end

def update
    @report.assign_attributes(report_params)
    authorize using: @report
    if @report.save
      redirect_to @report, notice: 'Report was successfully updated.'
    else
      render :edit
    end
 end

In complex cases, where we have to save the @report first to determine the associated City, we can wrap our controller action inside a database transaction that will be rolledback if authorize raises an exception. Examples of these 'complex cases' are:

• Callbacks that affect the instance's association to the scoping classes during the save lifecycle.
• Deep associations that rely on the creation of many intermediate instances to find out the resulting associated City.
• Overriding of ActiveRecord's update, save, create or similar methods that manipulate the instance's association to the scoping classes.
• Any other path / quirk / hack that does not allow ActiveRecord to pick up the association in memory.

def update
    ActiveRecord::Base.transaction do
        @report = Report.find(params[:id])
        if @report.update(report_params)
          authorize using: @report # Raises if not authorized
          redirect_to @report, notice: 'Report was successfully updated.'
        else
          render :edit
        end
     end
 end

Back to table of content

We can scope down the retrieval of collections to comply with the user's scoping rules using the apply_authz_scopes method.

For example, if we want to retrieve the Reports that are within the current_user's scoping rules for City and Department:

def index
    authorize skip_scoping: true
    @reports = apply_authz_scopes(on: Report) # Returns an AR relation
                 .includes(:user, :city, :clearance)
                 .order('cities.name ASC')
end

apply_authz_scopes takes a class or an ActiveRecord::Relation and applies the applicable scoping rules on top of the given argument. The method returns an ActiveRecord::Relation so it can be chained with other query methods.

apply_authz_scopes is also available as a view helper in case you need to use it inside a view.

Back to table of content

The authorized_path? view helper can be used to check if the current_user is authorized for a given url/path. Under the hood, Authz will ask your router for the controller and action in charge of resolving the given url/path and use that for determining authorization.

Similar to the authorize method above, we need to provide either a using: instance or skip_scoping: true if no sensible instance exists.

authorized_path? can be used to conditionally display parts of the view, most commonly a link_to.

<%= link_to 'Edit', edit_report_path(report) if authorized_path?(edit_report_path(report), using: report) %>
<%= link_to 'Destroy', report, { data: { confirm: 'Are you sure?' }, method: :delete } if authorized_path?(report_path(report), method: :delete, using: report) %>
<%= link_to('Create New Report', new_report_path) if authorized_path?(new_report_path, skip_scoping: true) %>

Back to table of content

The pattern of rendering a link only if the current_user is authorized to use it, is so common that it deserves it's own helper.

authz_link_to takes the same 3 arguments than Rail's link_to helper (i.e. name, options = {}, html_options = {}). Additionally you need to provide the using: instance to use against the scoping rules or skip_scoping: true if no sensible instance exists.

<%= authz_link_to 'Edit', edit_report_path(report), {}, using: report %>
<%= authz_link_to 'Destroy', report, { data: { confirm: 'Are you sure?' }, method: :delete }, using: report %>
<%= authz_link_to 'Create New Report', new_report_path, { class: 'button' }, skip_scoping: true %>
# Note that we are explictly wrapping the 3rd argument in {} to avoid ambiguity in the params.
# If you get an 'unknown keyword: class' error, it's caused by this.

Back to table of content

Everything that can be done through the admin GUI can also be done programmatically. You can interact with Authz’s models in the exact same way as you would interact with any ActiveRecord class.

The models you probably want to interact with are: Authz::ConrollerAction, Authz::BusinessProcess, Authz::Role, Authz::RoleGrant and Authz::ScopingRule.

You can also call user.roles to get the roles associated to a user.

If for some reason you want to reference a specific BusinessProces or Role from your code, you can do so through the code attribute. code is automatically set as the snake case of the name upon creation (unless you specify otherwise) and can't be changed from the GUI (so your code does not break if the name is changed).

Authz::Role.find_by(code: 'foo')
Authz::BusinessProcess.find_by(code: 'bar')

Back to table of content

Dynamic views based on the current_user's authorization privileges will add some calls to your database as part of the authorization resolution process. The effect of these additional calls can be significant in applications with highly dynamic views and requires special attention.

Authz implements 3 different caching strategies to meet production-grade performance needs.

Authz uses Active Record's SQL caching to guarantee that any query that is repeated during the request-response cycle is not re-run against your database. This is a built-in feature and as developer you don't have to do anything to benefit from it.

Some developers like to silence the logging from Active Record's CACHE as it can pollute your logs. Learn how to to that here.

Back to table of content

Cross-request caching allows Authz to build a cache that can be re-used across multiple requests, reducing sharply the number of authorization related calls to your database.

Authz's cross-request caching uses Rails' native ActiveSupport::Cache, which allows you to choose the caching store technology of your preference.

To enable this feature:

1. Configure caching as you would normally do for any Rails app. Read the official Rails Guide to find out how to do this.
2. Make sure you have enabled caching in development in order to try this feature locally. This can be toggled by running rails dev:cache on your terminal.
3. Go to config/initilizers/authz.rb and set config.cross_request_caching = true.

Back to table of content

Note:

There are only two hard things in Computer Science: cache invalidation and naming things. -- Phil Karlton

Many small and medium apps can work perfectly fine with cross-request caching. Correct cache invalidation for Fragment and Russian Doll caching can be difficult to achieve so don't fall prey to premature optimization.

Fragment and Russian Doll caching are common caching techniques where a fragment of pre-computed HTML is cached under a key. This key is used for retrieving the cached HTML instead of re-computing the fragment.

The cornerstone of this type of caching is key-based cache expiration , which means that they key must change whenever something that impacts the fragment's content changes. The key change will force the re-computation of the fragment, that will be stored in the cache under the new key.

Authorization information will most likely be a part of your keys whenever the fragment has content that depends on authorization (e.g. it contains authz_link_to or authorized_path?). You can use the #roles_cache_key method on your user instances to get a key that automatically changes whenever their role definitions have been modified.

Note that #roles_cache_key only contains information from the roles and does NOT contain information about the user. This means that if users alice and bob are both NY Sports Editor and SF Sports Writer:

• alice.roles_cache_key will contain information of both roles and the key will look something like this: "authz/roles/4-20190125101536064307/authz/roles/6-20190125084604920649"
• bob.roles_cache_key will return the same key. Therefore, if the fragment key does not depend on anything else, bob will re-use the cached information generated by alice.
• Whenever any of the role definitions change, the returned key will change, invalidating all fragments that depended on the role (e.g. a new business process is assigned to NY Sports Editor).
• If you need to make the fragment key depend on anything else, you need to include that yourself.

A typical fragment caching situation would look like this:

 - @reports.each do |report|
        - cache [report, current_user.roles_cache_key]
          tr
            td = report.id
            td = report.user.email
            td = report.department.try :name
            td = report.city.try :name
            td = report.title
            td = report.body.truncate(100)
            td = authz_link_to 'Show', report, using: report
            td = authz_link_to 'Edit', edit_report_path(report), using: report
            td = authz_link_to 'Destroy', report, { data: { confirm: 'Are you sure?' }, method: :delete }, using: report

Gotchas

The fact that 2 users have the same roles (and therefore the same #roles_cache_key) does not necessarily mean that they should be able to share cached fragments. For example, lets imagine that in our multi-city newspaper app we decide not to create separate Roles for each department (NY Sports Editor, NY Politics Editor). Instead we just create NY Editor role, storing in the departmets_users table the mapping between users and departments, and create a "mine" keyword inside ScopableByDepartment.

module ScopableByDepartment
  extend Authz::Scopables::Base
  
  def self.available_keywords
    %w[mine All]
  end
  
  def self.resolve_keyword(keyword, requester)
    if keyword == 'mine'
      requester.departments.pluck(:id) 
    end
  end
end

In this case, the NY Editor role will have configured the "mine" keyword for it's ScopableByDepartment rule. However, "mine" can resolve to different departments for alice and bob despite both being NY Editors. As a consequence, we need to include information about the departments in addition to #roles_cache_keyin the fragment keys.

Back to table of content

• When linking from your app into the Authz Admin, make sure you use the root_url helper and NOT the root_path. If you don't, you will get an ActionController::RoutingError No route matches.... In other words, if you mounted Authz as: authz in your router, use: authz_link_to 'Authorization Admin', authz.root_url, skip_scoping: true.

Back to table of content

Licensed under the MIT license, see the separate LICENSE.txt file.

Back to table of content