README.md
# AccessGranted [](https://codeclimate.com/github/pokonski/access-granted)
AccessGranted is a multi-role and whitelist based authorization gem for Rails. And it's lightweight (~300 lines of code)!
## Installation
Add the gem to your gemfile:
```ruby
gem 'access-granted', '~> 1.3'
```
Run the bundle command to install it. Then run the generator:
rails generate access_granted:policy
### Supported Ruby versions
Because it has **zero** runtime dependencies it is guaranteed to work on all supported MRI Ruby versions, see CI to check the up to date list.
It might and probably is working on Rubinius and JRuby but we are no longer testing against those.
## Summary
AccessGranted is meant as a replacement for CanCan to solve major problems:
1. Performance
On average AccessGranted is **20 times faster** in resolving identical permissions and takes less memory.
See [benchmarks](https://github.com/chaps-io/access-granted/blob/master/benchmarks).
2. Roles
Adds support for roles, so no more `if`s and `else`s in your Policy file. This makes it extremely easy to maintain and read the code.
3. Whitelists
This means that you define what the user can do, which results in clean, readable policies regardless of application complexity.
You don't have to worry about juggling `can`s and `cannot`s in a very convoluted way!
_Note_: `cannot` is still available, but has a very specifc use. See [Usage](#usage) below.
4. Framework agnostic
Permissions can work on basically any object and AccessGranted is framework-agnostic,
but it has Rails support out of the box. :)
It does not depend on any libraries, pure and clean Ruby code. Guaranteed to always work,
even when software around changes.
## Usage
Roles are defined using blocks (or by passing custom classes to keep things tidy).
**Order of the roles is VERY important**, because they are being traversed in top-to-bottom order.
At the top you must have an admin or some other important role giving the user top permissions, and as you go down you define less-privileged roles.
**I recommend starting your adventure by reading the [wiki page on how to start with Access Granted](https://github.com/chaps-io/access-granted/wiki/Role-based-authorization-in-Rails), where I demonstrate its abilities on a real life example.**
### Defining an access policy
Let's start with a complete example of what can be achieved:
```ruby
# app/policies/access_policy.rb
class AccessPolicy
include AccessGranted::Policy
def configure
# The most important admin role, gets checked first
role :admin, { is_admin: true } do
can :manage, Post
can :manage, Comment
end
# Less privileged moderator role
role :moderator, proc {|u| u.moderator? } do
can [:update, :destroy], Post
can :update, User
end
# The basic role. Applies to every user.
role :member do
can :create, Post
can [:update, :destroy], Post do |post, user|
post.author == user && post.comments.empty?
end
end
end
end
```
#### Defining roles
Each `role` method accepts the name of the role you're creating and an optional matcher.
Matchers are used to check if the user belongs to that role and if the permissions inside should be executed against it.
The simplest role can be defined as follows:
```ruby
role :member do
can :read, Post
can :create, Post
end
```
This role will allow everyone (since we didn't supply a matcher) to read and create posts.
But now we want to let admins delete those posts.
In this case we can create a new role above the `:member` to add more permissions for the admin:
```ruby
role :admin, { is_admin: true } do
can :destroy, Post
end
role :member do
can :read, Post
can :create, Post
end
```
The `{ is_admin: true }` hash is compared with the user's attributes to see if the role should be applied to it.
So, if the user has an attribute `is_admin` set to `true`, then the role will be applied to it.
**Note:** you can use more keys in the hash to check many attributes at once.
#### Hash conditions
Hashes can be used as matchers to check if an action is permitted.
For example, we may allow users to only see published posts, like this:
```ruby
role :member do
can :read, Post, { published: true }
end
```
#### Block conditions
Sometimes you may need to dynamically check for ownership or other conditions,
this can be done using a block condition in `can` method, like so:
```ruby
role :member do
can :update, Post do |post, user|
post.author_id == user.id
end
end
```
When the given block evaluates to `true`, then `user` is allowed to update the post.
#### Roles in order of importance
Additionally, we can allow admins to update **all** posts despite them not being authors like so:
```ruby
role :admin, { is_admin: true } do
can :update, Post
end
role :member do
can :update, Post do |post, user|
post.author_id == user.id
end
end
```
As stated before: **`:admin` role takes precedence over `:member`** role, so when AccessGranted sees that admin can update all posts, it stops looking at the less important roles.
That way you can keep a tidy and readable policy file which is basically human readable.
### Usage with Rails
AccessGranted comes with a set of helpers available in Ruby on Rails apps:
#### Authorizing controller actions
```ruby
class PostsController
def show
@post = Post.find(params[:id])
authorize! :read, @post
end
def create
authorize! :create, Post
# (...)
end
end
```
`authorize!` throws an exception when `current_user` doesn't have a given permission.
You can rescue from it using `rescue_from`:
```ruby
class ApplicationController < ActionController::Base
rescue_from "AccessGranted::AccessDenied" do |exception|
redirect_to root_path, alert: "You don't have permission to access this page."
end
end
```
You can also extract the action and subject which raised the error,
if you want to handle authorization errors differently for some cases:
```ruby
rescue_from "AccessGranted::AccessDenied" do |exception|
status = case exception.action
when :read # invocation like `authorize! :read, @something`
403
else
404
end
body = case exception.subject
when Post # invocation like `authorize! @some_action, Post`
"failed to access a post"
else
"failed to access something else"
end
end
```
You can also have a custom exception message while authorizing a request.
This message will be associated with the exception object thrown.
```ruby
class PostsController
def show
@post = Post.find(params[:id])
authorize! :read, @post, 'You do not have access to this post'
render json: { post: @post }
rescue AccessGranted::AccessDenied => e
render json: { error: e.message }, status: :forbidden
end
end
```
#### Checking permissions in controllers
To check if the user has a permission to perform an action, use the `can?` and `cannot?` methods.
**Example:**
```ruby
class UsersController
def update
# (...)
# only admins can elevate users to moderator status
if can? :make_moderator, @user
@user.moderator = params[:user][:moderator]
end
# (...)
end
end
```
#### Checking permissions in views
Usually you don't want to show "Create" buttons for people who can't create something.
You can hide any part of the page from users without permissions like this:
```erb
# app/views/categories/index.html.erb
<% if can? :create, Category %>
<%= link_to "Create new category", new_category_path %>
<% end %>
```
#### Customizing policy
By default, AccessGranted adds this method to your controllers:
```ruby
def current_policy
@current_policy ||= ::AccessPolicy.new(current_user)
end
```
If you have a different policy class or if your user is not stored in the `current_user` variable, then you can override it in any controller and modify the logic as you please.
You can even have different policies for different controllers!
### Usage with pure Ruby
Initialize the Policy class:
```ruby
policy = AccessPolicy.new(current_user)
```
Check the ability to do something:
with `can?`:
```ruby
policy.can?(:create, Post) #=> true
policy.can?(:update, @post) #=> false
```
or with `cannot?`:
```ruby
policy.cannot?(:create, Post) #=> false
policy.cannot?(:update, @post) #=> true
```
## Common examples
### Extracting roles to separate files
Let's say your app is getting bigger and more complex. This means your policy file is also getting longer.
Below you can see an extracted `:member` role:
```ruby
class AccessPolicy
include AccessGranted::Policy
def configure
role :administrator, is_admin: true do
can :manage, User
end
role :member, MemberRole, -> { |user| !u.guest? }
end
end
```
And roles should look like this:
```ruby
# app/roles/member_role.rb
class MemberRole < AccessGranted::Role
def configure
can :create, Post
can :destroy, Post do |post, user|
post.author == user
end
end
end
```
## Compatibility with CanCan
This gem has been created as a replacement for CanCan and therefore it requires minimum work to switch.
### Main differences
1. AccessGranted does not extend ActiveRecord in any way, so it does not have the `accessible_by?`
method which could be used for querying objects available to current user.
This was very complex and only worked with permissions defined using hash conditions, so
I decided to not implement this functionality as it was mostly ignored by CanCan users.
2. Both `can?`/`cannot?` and `authorize!` methods work in Rails controllers and views, just like in CanCan.
The only change you have to make is to replace all `can? :manage, Class` with the exact action to check against.
`can :manage` is still available for **defining** permissions and serves as a shortcut for defining `:create`, `:read`, `:update`, `:destroy` all in one line.
3. Syntax for defining permissions in the AccessPolicy file (Ability in CanCan) is exactly the same,
with roles added on top. See [Usage](#usage) above.
## Contributing
1. Fork it
2. Create your feature branch (`git checkout -b my-new-feature`)
3. Commit your changes (`git commit -am 'Add some feature'`)
4. Push to the branch (`git push origin my-new-feature`)
5. Create new pull request