An awesome authorization system
Add this line to your application's Gemfile:
gem 'scram'
And then execute:
$ bundle
Or install it yourself as:
$ gem install scram
Click here to see YARD Documentation
- Holder
- Scram doesn't force you to use a specific group system. Instead, just include
Holder
into any class which can holdPolicies
. - Scram provides a class for objects like Groups through an
AggregateHolder
. This is a class which should be included in anything which holds policies through other holders. - In most cases, your
AggregateHolder
will be aUser
model. YourGroup
model will be aHolder
. If you don't want to use a group system, then yourUser
model will likely be aHolder
.
- Scram doesn't force you to use a specific group system. Instead, just include
- Policy
- Policies are used to bundle together permissions.
- There are 2 kinds of
Policies
: Those for a specific model, and "global"Policies
for permissions that aren't bound to a specific model.
- Target
Targets
are a way to declare what actions are allowed in aPolicy
.Targets
have a list of actions and conditions.- Actions are anything a user can do to an object. For example:
:update, :view, :create, :destroy
. - Conditions are used to refine what instances a target applies to. They support basic comparisons to attributes, but can be used to support more complex logic with the DSL.
- Actions are anything a user can do to an object. For example:
If you choose to implement Holder into your user class directly, it may look something like the following.
class User
...
include Scram::Holder
# Will automatically implement the needed #policies method for Holder.
has_many :policies, class: "Scram::Policy"
def scram_compare_value
self.id
end
end
This sort of system would not include a group system at all (for simplicity). If you want a Group system, have your user include Scram::AggregateHolder
and then implement #aggregates
to return your groups (which should be Holder
s themselves).
We will be providing a full fledge example application of Scram shortly which will include a Group and membership system, and will clarify how the AggregateHolder
system works. For now, lets see how Scram works in its simplest usage (a user who stores policies just for themselves).
Now lets add a String permission to display a statistics bar for users like admins. We want to call user.can? :view, "peek_bar"
and have it return true for admins.
To do this, we'll need to define a non-model Policy (because our object is a string, "peek_bar").
user = ...
policy = Scram::Policy.new
policy.name = "global-strings-policy" # Note that we're setting name, and we will leave context nil.
policy.context = nil # This would be nil by default as well. By not setting this to anything, we let this Policy handle String permissions, and not be bound to a model.
policy.save
user.policies << policy
user.save
Now we want to add a target that represents the ability to view "peek_bar"
.
target = Target.new
target.conditions = {:equals => { :'*target_name' => "peek_bar"}}
target.actions << "view"
policy.targets << target
policy.save
This code creates a target which permits viewing if the *target_name
equals "peek_bar".
Scram automatically replaces *target_name
with the action being compared. For example, in can? :view, "something_else"
Scram would check if "something_else" == "peek_bar"
.
And now we're done! π
Now lets add something a bit more complex. Say we're developing a Forum application. We want to add the ability for a user to edit their own Posts
using Scram.
Here's our simple Post
model:
class Post
...
belongs_to :user
end
Lets make a Policy that handles post related permissions.
user = ...
policy = Scram::Policy.new
policy.name = "Post Stuff" # This name is just for organizational/display purposes
policy.context = Post.to_s # Note: By setting context, we bind this policy to the model "Post"
policy.save
user.policies << policy
user.save
Now we need a Target in our Policy to let users edit their own Posts.
target = Target.new
target.conditions = {:equals => {:user => "*holder"}}
target.actions << "edit"
policy.save
What is *holder
? Well, Scram replaces this special variable with the current user being compared. In User#scram_compare_value
we return the User's ObjectId, and this is exactly what Scram replaced *holder
with.
So now this Target reads "allow a holder to edit a Post if the user of that Post is the holder". Pretty neat, huh?
And now we're done! Go ahead and call holder.can? :edit, @post
on a post which they own, and you'll see that Scram allows it! π
In our last example, we let Scram directly compare an attribute of the model. What if we need more complex checking behavior? Luckily, Scram provides a DSL for models to easily define conditions which can be referenced in the database in place of attributes.
Lets revisit the Post
example, but this time we'll define how to get the owner using a condition DSL, instead of the attribute.
class Post
include Scram::DSL::ModelConditions
...
belongs_to :user
scram_define do
condition :owner do |post|
post.user
end
end
end
Now we no longer need to directly tell our Target to access the user field. Here's what the equivalent Target would look like from our previous example, now using the new condition:
...
target.conditions = {:equals => {:'*owner' => "*holder"}}
...
Scram is smart enough to realize that any key starting with an *
, like *owner
, is a manually defined condition. Now, calling user.can? :edit, @post
will compare the value returned by the condition
block to the hash value (which in this case is the Holder).
You may have noticed from the previous examples that the keys of our Target conditions were things like equals
and less_than
. These come from our Comparator definitions (see Scram::DSL::Definitions::COMPARATORS
).
These comparators are defined using the DSL for comparators. We provide a basic set of comparing operators, but you may need to add your own. To do this, we recommend creating an initializer file and then calling something like the following:
builder = Scram::DSL::Builders::ComparatorBuilder.new do
comparator :asdf do |a,b|
true
end
end
Scram::DSL::Definitions.add_comparators(builder)
Now your targets can use asdf
as a conditions key, and Scram will use your method of comparison to determine if something is true or not. In this case, asdf
returns true regardless of the two objects being compared.
Having trouble trying to use a holder check on a relation? Easy fix! The issue you are experiencing is just that the holder's scram_compare_value will probably be an ObjectId of some sort, but if you are comparing it against the relation... you are trying to compare the current holder's ObjectId to a document. The fix to this is just defining a condition within the model with the user you are trying to compare, and returning the object id of that.
Example of the issue:
Lets say your Post
model belongs_to :user
. If you tried setting up a condition which checks something like this: :equals => { :'user' => "*holder" }
it will never work because of the above description. To fix it, define a condition which returns an ObjectId.
scram_define do
condition :owner do |post|
post.user.scram_compare_value # we could also have done post.user.id
end
end
Now update your Target to have the following condition: :equals => { :'*owner' => "*holder" }
. Voila! It will all work now, because you are correctly comparing the right data types.
After checking out the repo, run bin/setup
to install dependencies. Then, run rake spec
to run the tests. You can also run bin/console
for an interactive prompt that will allow you to experiment.
To install this gem onto your local machine, run bundle exec rake install
. To release a new version, update the version number in version.rb
, and then run bundle exec rake release
, which will create a git tag for the version, push git commits and tags, and push the .gem
file to rubygems.org.
Bug reports and pull requests are welcome on GitHub at https://github.com/skreem/scram.