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OmniAuth adapter to allow apps to sign in via GOV.UK signon


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This gem provides everything needed to integrate an application with Signon. It's a wrapper around OmniAuth that adds a 'strategy' for oAuth2 integration against Signon, and the necessary controller to support that request flow.

Some of the applications that use this gem:


Integration with a Rails 4+ app

  • Include the gem in your Gemfile:

    gem 'gds-sso'
  • Create a "users" table in the database: (example migration with all the necessary fields)

  • Create a User model with the following:

    serialize :permissions, Array
  • Add to your ApplicationController:

    include GDS::SSO::ControllerMethods
    before_action :authenticate_user!

Securing your application

GDS::SSO::ControllerMethods provides some useful methods for your application controllers.

To make sure that only people with a signon account and permission to use your app are allowed in use authenticate_user!.

class ApplicationController < ActionController::Base
  include GDS::SSO::ControllerMethods
  before_action :authenticate_user!
  # ...

You can refine authorisation to specific controller actions based on permissions using authorise_user!. All permissions are assigned via Signon.

class PublicationsController < ActionController::Base
  include GDS::SSO::ControllerMethods
  before_action :authorise_for_editing!, except: [:show, :index]
  # ...
  def authorise_for_editing!

authorise_user! can be configured to check for multiple permissions:

# fails unless the user has at least one of these permissions
authorise_user!(any_of: %w(edit create))

# fails unless the user has both of these permissions
authorise_user!(all_of: %w(edit create))

The signon application makes sure that only users who have been granted access to the application can access it (e.g. they have the signin permission for your app).

Authorisation for API Users

In addition to the single-sign-on strategy, this gem also allows authorisation via a "bearer token". This is used by publishing applications to be authorised as an API user.

To authorise with a bearer token, a request has to be made with the header:

# See
Authorization: Bearer your-token-here

To avoid making these requests for each incoming request, this gem will automatically cache a successful response, using the Rails cache.

If you are using a Rails 5 app in api_only mode this gem will automatically disable the oauth layers which use session persistence. You can configure this gem to be in api_only mode (or not) with:

GDS::SSO.config do |config|
  # ...
  # Only support bearer token authentication and send responses in JSON
  config.api_only = true

Use in production mode

To use gds-sso in production you will need to setup the following environment variables, which we look for in the config. You will need to have admin access to Signon to get these.


Use in development mode

In development, you generally want to be able to run an application without needing to run your own SSO server to be running as well. GDS-SSO facilitates this by using a 'mock' mode in development. Mock mode loads an arbitrary user from the local application's user tables:

GDS::SSO.test_user || GDS::SSO::Config.user_klass.first

To make it use a real strategy (e.g. if you're testing an app against the signon server), you will need to ensure that your Signon database has got OAuth config that matches what the apps use in development mode. To do this, run this in Signon:

bundle exec ./script/make_oauth_work_in_dev

Once that's done, set an environment variable when you run your app. e.g.:

GDS_SSO_STRATEGY=real bundle exec rails s

Extra permissions for api users

By default the mock strategies will create a user with signin permission.

If your application needs different or extra permissions for access, you can specify this by adding the following to your config:

GDS::SSO.config do |config|
  # other config here
  config.additional_mock_permissions_required = ["array", "of", "permissions"]

The mock bearer token will then ensure that the dummy api user has the required permission.

Testing in your application

If your app is using test-unit or minitest, there is a linting test that can verify your User model is compatible with GDS:SSO::User:

require 'gds-sso/lint/user_test'

class GDS::SSO::Lint::UserTest
  def user_class

Or if your app is using rspec, there is a shared examples spec:

require 'gds-sso/lint/user_spec'

describe User do
  it_behaves_like "a gds-sso user class"

Running the test suite

Run the tests with:

bundle exec rake


MIT License