Rack-CAS Build Status Gem Version

Rack-CAS is simple Rack middleware to perform CAS client authentication.


  • Rack based
  • Framework independent Works with, but doesn't depend on Rails, Sinatra, etc.
  • Minimal dependencies Current gem dependencies are rack, addressable and nokogiri.
  • Supports CAS extra attributes Extra attributes are a mess though. So let me know if your brand of CAS server isn't supported.
  • Single sign out One of the included session stores must be used.
  • Rake tasks to prune stale sessions rack_cas:sessions:prune:active_record and rack_cas:sessions:prune:mongoid




Add gem 'rack-cas' to your Gemfile and run bundle install

Once the necessary gems have been installed, in your config/application.rb add:

config.rack_cas.server_url = 'https://cas.example.com/'

If the the server URL depends on your environment, you can define it in the according file: config/environments/<env>.rb


Since protocol p3 the protocol is prepended in certain urls. If you wish to use protocol p3 set the following config variable

config.rack_cas.protocol = 'p3'

For more info

Single Logout

If you wish to enable single logout you'll need to modify your configuration as below.

Active Record

Set the session_store in your config/application.rb:

require 'rack-cas/session_store/active_record'
config.rack_cas.session_store = RackCAS::ActiveRecordStore

Edit your config/initializers/session_store.rb file with the following:

require 'rack-cas/session_store/rails/active_record'
Rails.application.config.session_store ActionDispatch::Session::RackCasActiveRecordStore


rails generate cas_session_store_migration
rake db:migrate


Set the session_store in your config/application.rb:

require 'rack-cas/session_store/mongoid'
config.rack_cas.session_store = RackCAS::MongoidStore

Edit your config/initializers/session_store.rb file with the following:

require 'rack-cas/session_store/rails/mongoid'
YourApp::Application.config.session_store ActionDispatch::Session::RackCasMongoidStore

Sinatra and Other Rack-Compatible Frameworks

Add gem 'rack-cas' to your Gemfile and run bundle install

Add the following to your config.ru file:

require 'rack/cas'
use Rack::CAS, server_url: 'https://login.example.com/cas'

See the example Sinatra app to get started.

Single Sign Out

You will need to store sessions in session store supported by Rack CAS.

Active Record

Add a migration that looks roughly like

class AddSessionStore < ActiveRecord::Migration
    def change
        create_table :sessions do |t|
            t.string :cas_ticket
            t.string :session_id
            t.text :data
            t.datetime :created_at
            t.datetime :updated_at

Then use the middleware with

require 'rack-cas/session-store/rack/active_record'
use Rack::Session::RackCASActiveRecordStore


Extra Attributes

You can whitelist which extra attributes to keep. In your config/application.rb:

config.rack_cas.extra_attributes_filter = %w(some_attribute some_other_attribute)

Excluding Paths

If you have some parts of your app that should not be CAS authenticated (such as an API namespace), just pass exclude_path to the middleware. You can pass in a string that matches the beginning of the path, a regular expression or an array of strings and regular expressions.

use Rack::CAS, server_url: '...', exclude_path: '/api'
use Rack::CAS, server_url: '...', exclude_path: /\.json/
use Rack::CAS, server_url: '...', exclude_paths: ['/api', /\.json/]

The same options can be passed to FakeCAS.

use Rack::FakeCAS, exclude_path: '/api'

Excluding Requests

If the path exclusion is not suitable to ignore the CAS authentication in some parts of your app, you can pass exclude_request_validator to the middleware with a custom validator. You need to pass a Proc object that will accept a Rack::Request object as a parameter.

use Rack::CAS, server_url: '...', exclude_request_validator: Proc.new { |req| req.env['HTTP_CONTENT_TYPE'] == 'application/json' }

Ignore 401 Intercept

For some requests you might want to ignore the 401 intercept made by the middleware. For example when we want CAS to authenticate API requests but leave the redirect handling to the client. For this you can use the ignore_intercept_validator. You need to pass a Proc object that will accept a Rack::Request object as a parameter.

use Rack::CAS, server_url: '...', ignore_intercept_validator: Proc.new { |req| req.env['HTTP_CONTENT_TYPE'] == 'application/json' }
use Rack::CAS, server_url: '...', ignore_intercept_validator: Proc.new { |req| req.env['PATH_INFO'] =~ 'api' }

SSL Cert Verification

If you're working in development or staging your CAS server may not have a legit SSL cert. You can turn off SSL Cert verification by adding the following to config/application.rb.

config.rack_cas.verify_ssl_cert = false

CAS Login Renew Flag

The CAS standard allows for a renew=true parameter to be passed to the CAS server which will force the user to re-login every time CAS authentication is performed, for added security. To enable this for your application, add the following to config/application.rb.

config.rack_cas.renew = true


Your app should return a 401 status whenever a request is made that requires authentication. Rack-CAS will catch these responses and attempt to authenticate via your CAS server.

Once authentication with the CAS server has completed, Rack-CAS will set the following session variables:

request.session['cas']['user'] #=> johndoe
request.session['cas']['extra_attributes'] #=> { 'first_name' => 'John', 'last_name' => ... }

NOTE: extra_attributes will be an empty hash unless they've been configured on your CAS server.


Controller Tests

Testing your controllers and such should be as simple as setting the session variables manually in a helper.

def set_current_user(user)
  session['cas'] = { 'user' => user.username, 'extra_attributes' => {} }

Integration Tests

Integration testing using something like Capybara is a bit trickier because the session can't be manipulated directly. So for integration tests, I recommend using the provided Rack::FakeCAS middleware instead of Rack::CAS.

require 'rack/fake_cas'
use Rack::FakeCAS

In addition you can pass a Hash to configure extra attributes for predefined usernames.

use Rack::FakeCAS, {}, {'john' => {'name' => 'John Doe'}}

If you are using Rails, FakeCAS is automatically used in the test environment by default. If you would like to activate it in any other environment, add the following to the corresponding config/environments/<env>.rb:

config.rack_cas.fake = true

You can also configure extra attribute mappings through the Rails config:

config.rack_cas.fake_attributes = { 'john' => { 'name' => 'John Doe' } }

Then you can simply do the following in your integration tests in order to log in.

visit '/restricted_path'
fill_in 'username', with: 'johndoe'
fill_in 'password', with: 'any password'
click_button 'Login'

NOTE: The FakeCAS middleware will authenticate any username with any password and so should never be used in production.