Note:

This branch is maintained for Rails v6.* and Ruby v2.6.* for Rails v5.* please use rails-5 branch.

ACU is the acronym for Access Control Unit, and it's designed to give the 100% control over permissions on multiple levels of rails application's structure. The software engineering of this gem tends to make it much faster and simple. All you have to do is to define the entities of your authentications (i.e what is who?) and write the rules for them based on allow/deny binary logic, and everything else will be done automatically.

Add this line to your application's Gemfile:

gem 'rails-acu'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rails-acu

Then install it in you app using:

$ rails generate acu:install

After installation using rails generate acu:install two files will be created:

create  config/initializers/acu_setup.rb
create  config/initializers/acu_rules.rb

The file acu_setup.rb is the configuration of ACU gem, you can leave it alone and use the default configurations or customize it as desired, we will talk about the configuration later.

The other hand the acu_rules.rb is where you put your access rules there, access rules are binary, either an entity can access a resource or not - in this gem, resource means any of namespace, controller and action. here as an example acu_rules.rb and we explain its components in the following:

# config/initializers/acu_rules.rb
Acu::Rules.define do
  # anyone makes a request could be count as everyone!
  whois(:everyone) { true }

  whois(:admin, args: [:user]) { |c| c and c.user_type == :ADMIN.to_s }

  whois(:client, args: [:user]) { |c| c and c.user_type == :PUBLIC.to_s }

  # admin can access to everywhere
  allow :admin

  # the default namespace
  namespace do  
    # assume anyone can access, your default namespace
    allow :everyone
    controller :home, :shop do
      allow :admin, :client, on: [:some_secret_action1, :some_secret_action2]
      # OR
      # action :some_secret_action1, :some_secret_action2 do
      #  allow :admin, :client
      # end
    end
  end

  # allow every get access to public controller in 3 [default(the `nil`), admin]
  namespace nil, :admin do
    controller :public do
      allow :everyone
    end
  end

  # the admin namespace
  namespace :admin do

    controller :contact, only: [:send_message] do
      allow :everyone
    end

    controller :contact do
      action(:support) {
        allow :client
      }
    end
  end

  # nested namespace (since v3.0.0)
  namespace :admin do
    namespace :chat do
      allow :client
    end
  end

  # negated entities (since v3.0.4)
  namespace do
    controller :profile do
      # only owners can edit the profile page
      deny :not_owner, on: [:edit]
    end
  end
end

As we define our rules at the first line, we have to say who are the entities? to whom we call who? for this purpose I have come up with a simple entity definition whois, it takes three arguments (1 of them is optional: args), first the label of the entity, in this example they are :everyone, :admin and :client, the second argument (which is optional) is the variables that are going to be used to determining if the current request has been initiated by the entity or not, and the final argument is a block which its job is to determine who is the defined entity!

Once we defined our entities we can set their binary access permissions at namespace/controller/action levels using allow and deny helpers. that is it, we are done tutorialing; from now on is just tiny details. :)

Scenario: We have a public site which serves to its client's; we have 2 namespaces on this site, one is the default namespace with home controller in it, and the second namespace belongs to the admin of site which has many controllers and also a contact controller.
We want to grant access to everyone for all of home controller actions in default namespace except the some_secret_action1 and some_secret_action2; but these some_secret_action* can be accessed via the :admin and :client entities. By default only :admin can access to everywhere, but in namespace admin we made an exception for 2 actions in the Admin::ContactController which everyone can send_message to the admin and only clients can ask for support. Finally we want to grant access to everyone for public controllers in our 2 namespaces the default and admin. Also clients can access to everything in namespace chat.
If you back trace it in the above example you can easily find this scenario in the rules, plain and simple.

For gaurding you application using ACU, you to need to call it in before_action callbacks (preferably in you base controller). And also occasionally there is some situation that you need to pass the some argument in the entities to be able to determine the entity (i.e you cannot get it from session, global variables/function or directly from database) for such situations you can pass the arguments as you are calling Acu::Monitor.gaurd in your before_action as below:

class ApplicationController < ActionController::Base
  protect_from_forgery with: :exception

  before_action { Acu::Monitor.gaurd by: { user: some_way_to_fetch_it } }
end

The method Acu::Monitor.gaurd accepts a hashed list of agruments named by, please note that the keys should be identical to the entities' args argument.

Although you can define a binary allow/deny access rule in the acu_rules.rb file but there will be some gray area that neither you can allow full access to the resource nor no access.
For those situations you allow the entities to get access but limits their operations in the action/view/layout with the acu_is?, acu_as and acu_except helpers, here is some usage example of them:

# return true if the entity `:admin`'s block in `whois(:admin)` return true, otherwise false
acu_is? :admin
# returns true if any of the given entity's block return true; if none of the was valid, returns false.
acu_is? [:admin, :client]

# executes the block if current user identified as an admin by `whois(:admin)`
acu_as :admin do
  puts 'You are identified as an `admin`'
end
# executes the block if current user identified as either `:admin` or `:client`
acu_as [:admin, :client] do
  puts 'You are either `admin` or `client`'
end

# DO NOT execute the block if current user identified as `:guest`
acu_except [:guest] do
  puts 'Except `:guest`s anyone else can execute this code'
end

# [since version v4.1.0]
# alias checking:
#   passing dynamic params to check if the passed params identify as an entity or not!
#   NOTE: the passed arguments should match the entity definition arguments  

# checks if the given user is an `admin` entity or not?
acu_is? :admin, user: User.find_by_username('username')
# checks if the given user is an `admin` OR a `client` entity or not?
acu_is? [:admin, :client], user: User.find_by_username('username')
# execute the block if the passed user is an `admin`
acu_as :admin, user: User.find_by_username('username') do
    puts 'The `username` is an `admin`'
end
# DO NOT execute the block if passed user identified as `:guest`
acu_except [:guest], user: User.find_by_username('username') do
  puts 'Except `:guest`s anyone else can execute this code'
end

One of the files that acu:install command will generate is acu_setup.rb which contains the configuration for the gem, the default configurations are as following:

Acu.setup do |config|
  # to tighten the security this is enabled by default
  # i.e if it checked to be true, then if a request didn't match to any of rules, it will get passed through
  # otherwise the requests which don't fit into any of rules, the request is denied by default
  config.allow_by_default = false

  # the audit log file, to log how the requests handles, good for production
  # leave it black for nil to disable the logging
  config.audit_log_file   = ""

  # cache the rules to make rule matching much faster
  # it's not recommended to use it in developement/test evn.
  config.use_cache = false

  # the caching namespace
  config.cache_namespace = 'acu'

  # define the expiration of cached entries
  config.cache_expires_in = nil

  # the race condition ttl
  config.cache_race_condition_ttl = nil

  # more details about cache options:
  # http://guides.rubyonrails.org/caching_with_rails.html
end

Here are the details of the configurations:

Here are the list of APIs that didn't mentioned above:

Here are the list of exceptions defined in ACU gem:

class Acu::Errors::AccessDenied < StandardError

class Acu::Errors::UncheckedPermissions < StandardError

class Acu::Errors::InvalidSyntax < StandardError

class Acu::Errors::AmbiguousRule < StandardError

class Acu::Errors::InvalidData < StandardError

class Acu::Errors::MissingData < InvalidData

class Acu::Errors::MissingEntity < MissingData

class Acu::Errors::MissingUser < MissingData

class Acu::Errors::MissingAction < MissingData

class Acu::Errors::MissingController < MissingData

class Acu::Errors::MissingNamespace < MissingData

Consider we have to give the everyone to access the default namespace except :profile controller which will only allow by signed in users, although there are tools provided for this purpose, such as except and only tags on controller and namespace but it would be nice if there are such a command like override which its skeleton has been defined in the Acu::Rules.override which enables the previously defined rule to be overrided, the following pseudo-example removes the allow :everyone rule from the controller profile:

  # config/initializers/acu_rules.rb
  [...]
  namespace do
    allow :everyone
    controller :profiles do
      override :everyone
      allow :signed_in
    end
  end
  [...]

• Moved to Rails 6 & Ruby 2.6.
• More effective & robust permission caching & checking.

• Nested namespace support

• Core functionalities implemented and stabilized

In order contributing to this project:

1. Fork
2. Make changes/upgrades/fixes etc
3. Write a through tests
4. Make a pull request to the develop branch

The gem is available as open source under the terms of the MIT License.