OmniAuth::Oidc

This gem provides an OmniAuth strategy for integrating OpenID Connect (OIDC) authentication into your Ruby on Rails application. It allows seamless login using various OIDC providers.

Developed with reference to omniauth-openid-connect and omniauth_openid_connect.

Article on Medium about the development of this gem.

Installation

To install the gem run the following command in the terminal:

$ bundle add omniauth_oidc

If bundler is not being used to manage dependencies, install the gem by executing:

$ gem install omniauth_oidc

Usage

To use the OmniAuth OIDC strategy, you need to configure your Rails application and set up the necessary environment variables for OIDC client credentials.

Configuration

You have to provide Client ID, Client Secret and url for the OIDC configuration endpoint as a bare minimum for the omniauth_oidc to work properly.
Create an initializer file at config/initializers/omniauth.rb

# config/initializers/omniauth.rb
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :oidc, {
    name: :simple_provider, # used for dynamic routing
    client_options: {
      identifier: '23575f4602bebbd9a17dbc38d85bd1a77',
      secret: ENV['SIMPLE_PROVIDER_CLIENT_SECRET'],
      config_endpoint: 'https://simpleprovider.com/cdn-cgi/access/sso/oidc/23575f4602bebbd9a17dbc38d85bd1a77/.well-known/openid-configuration'
    }
  }
end

With Devise

Devise.setup do |config|
  config.omniauth :oidc, {
    name: :simple_provider,
    scope: [:openid, :email, :profile, :address],
    response_type: :code,
    uid_field: "preferred_username",
    client_options: {
      identifier: '23575f4602bebbd9a17dbc38d85bd1a77',
      secret: ENV['SIMPLE_PROVIDER_CLIENT_SECRET'],
      config_endpoint: 'https://simpleprovider.com/cdn-cgi/access/sso/oidc/23575f4602bebbd9a17dbc38d85bd1a77/.well-known/openid-configuration'
    }
  }
end

The gem also supports a wide range of optional parameters for higher degree of configurability.

# config/initializers/omniauth.rb
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :oidc, {
    name: :complex_provider, # used for dynamic routing
    issuer: 'https://complexprovider.com/cdn-cgi/access/sso/oidc/23575f4602bebbd9a17dbc38d85bd1a77',
    scope: [:openid],
    response_type: 'id_token',
    require_state: true,
    response_mode: :query,
    prompt: :login,
    send_nonce: false,
    uid_field: "sub",
    pkce: false,
    client_options: {
      identifier: '23575f4602bebbd9a17dbc38d85bd1a77',
      secret: ENV['COMPLEX_PROVIDER_CLIENT_SECRET'],
      config_endpoint: 'https://complexprovider.com/cdn-cgi/access/sso/oidc/23575f4602bebbd9a17dbc38d85bd1a77/.well-known/openid-configuration',
      host: 'complexprovider.com'
      scheme: "https",
      port: 443,
      authorization_endpoint: 'https://complexprovider.com/cdn-cgi/access/sso/oidc/23575f4602bebbd9a17dbc38d85bd1a77/authorization',
      token_endpoint: 'https://complexprovider.com/cdn-cgi/access/sso/oidc/23575f4602bebbd9a17dbc38d85bd1a77/token',
      userinfo_endpoint: 'https://complexprovider.com/cdn-cgi/access/sso/oidc/23575f4602bebbd9a17dbc38d85bd1a77/userinfo',
      jwks_uri: 'https://complexprovider.com/cdn-cgi/access/sso/oidc/23575f4602bebbd9a17dbc38d85bd1a77/jwks',
      end_session_endpoint: '/signout'
    }
  }
end

Ensure to replace identifier, secret, configuration endpoint url and others with credentials received from your OIDC provider.

Redirecting for Authentication

Buttons and links to initialize the authentication request can be placed on relevant pages as below:

<%= button_to "Login with Simple Provider", "/auth/simple_provider" %>

Handling Callbacks

The gem uses dyanmic routes to handle different phases, and while you can use same routes in your Rails application, for
better experience you should have a controller to process the authenticated user. Create a CallbacksController:

# app/controllers/callbacks_controller.rb
class CallbacksController < ApplicationController
  def omniauth
    # user info received from OIDC provider will be available in `request.env['omniauth.auth']`
    auth = request.env['omniauth.auth']

    user = User.find_or_create_by(uid: auth['uid']) do |user|
      user.name = auth['info']['name']
      user.email = auth['info']['email']
    end

    session[:user_id] = user.id
    redirect_to root_path, notice: 'Successfully logged in!'
  end
end

Routes

The gem uses dynamic routes when making requests to the OIDC provider endpoints. These routes follow the naming pattern
of https://your_app.com/auth//callback, where `is the provider name defined
within the configuration of theomniauth.rb` initializer.

Dynamic routes are used to process responses and perform intermediary steps by the middleware, e.g. request phase,
token verification. While you can define and use same routes within your Rails app, you can modify your routes.rb
to perform a dynamic redirect to a another controller method. In an example below, all OIDC responses are ultimately
redirected to the omniauth method of the callbacks_controller, which is a universal method to handle authentication
with various omniauth providers:

# config/routes.rb
Rails.application.routes.draw do
  match 'auth/:provider/callback', via: :get, to: "callbacks#omniauth"
end

Alternatively, you can specify separate redirects for some of your OIDC providers, in case you need to handle responses
differently:

# config/routes.rb
Rails.application.routes.draw do
  match 'auth/simple_provider/callback', via: :get, to: "callbacks#simple_provider"
  match 'auth/complex_provider/callback', via: :get, to: "callbacks#complex_provider"

  # you can add the line below if you would like the rest of the providers to be redirected to a universal `omniauth` method
  match 'auth/:provider/callback', via: :get, to: "callbacks#omniauth"
end

Please note that you should register https://your_app.com/auth//callback with your OIDC provider
as a callback redirect url.

Using Access Token Without User Info

In case your app requries only an access token and not the user information, then you can specify an optional
configuration in the omniauth initializer:

# config/initializers/omniauth.rb
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :oidc, {
    name: :simple_provider_access_token_only,
    fetch_user_info: false, # if not specified, default value of true will be applied
    client_options: {
      identifier: '23575f4602bebbd9a17dbc38d85bd1a77',
      secret: ENV['SIMPLE_PROVIDER_CLIENT_SECRET'],
      config_endpoint: 'https://simpleprovider.com/cdn-cgi/access/sso/oidc/23575f4602bebbd9a17dbc38d85bd1a77/.well-known/openid-configuration'
    }
  }
end

Then the callback returned once your user authenticates with the OIDC provider will contain only access token parameters:

# app/controllers/callbacks_controller.rb
class CallbacksController < ApplicationController
  def omniauth
    # access token parameters received from OIDC provider will be available in `request.env['omniauth.auth']`
    omniauth_params = request.env['omniauth.auth']

    # omniauth_params will contain similar data as shown below
    # {"provider"=>:simple_provider_access_token_only,
    #  "credentials"=>
    #   {"id_token"=> "id token value",
    #    "token"=> "token value",
    #    "refresh_token"=>"refresh token value",
    #    "expires_in"=>300,
    #    "scope"=>nil
    #   }
    # }
  end
end

Advanced Configuration

You can customize the OIDC strategy further by adding additional configuration options:

Field	Description	Required	Default Value	Example/Notes
name	Arbitrary string to identify OIDC provider and segregate it from other OIDC providers	no	"oidc"	:simple_provider
issuer	Root url for the OIDC authorization server	no	retrived from config_endpoint	"https://simpleprovider.com"
fetch_user_info	Fetches user information from user_info_endpoint using the access token. If set to false the omniauth params will include only access token	no	true	fetch_user_info: false
client_auth_method	Authentication method to be used with the OIDC authorization server	no	:basic	"basic", "jwks"
scope	OIDC scopes to be included in the server’s response	[:openid] is required	all scopes offered by OIDC provider	[:openid, :profile, :email]
response_type	OAuth2 response type expected from OIDC provider during authorization	no	"code"	"code" or "id_token"
state	Value to be used for the OAuth2 state parameter on the authorization request. Can be a proc that generates a string	no	Random 16 character string	Proc.new { SecureRandom.hex(32) }
require_state	Boolean to indicate if state param should be verified. This is a recommendation by OIDC spec	no	true	true or false
response_mode	The response mode per OIDC spec	no	nil	:query, :fragment, :form_post or :web_message
display	Specifies how OIDC authorization server should display the authentication and consent UI pages to the end user	no	nil	:page, :popup, :touch or :wap
prompt	Specifies whether the OIDC authorization server prompts the end user for reauthentication and consent	no	nil	:none, :login, :consent or :select_account
send_scope_to_token_endpoint	Should the scope parameter be sent to the authorization token endpoint	no	true	true or false
post_logout_redirect_uri	Logout redirect uri to use per the session management draft	no	nil	"https://your_app.com/logout/callback"
uid_field	Field of the user info response to be used as a unique ID	no	'sub'	"sub" or "preferred_username"
extra_authorize_params	Hash of extra fixed parameters that will be merged to the authorization request	no	{}	{"tenant" => "common"}
allow_authorize_params	List of allowed dynamic parameters that will be merged to the authorization request	no	[]	[:screen_name]
pkce	Enable PKCE flow	no	false	true or false
pkce_verifier	Specify custom PKCE verifier code	no	Random 128-character string	Proc.new { SecureRandom.hex(64) }
pkce_options	Specify custom implementation of the PKCE code challenge/method	no	SHA256(code_challenge) in hex	Proc to customise the code challenge generation
client_options	Hash of client options detailed below in a separate table	yes	see below	see below
jwt_secret_base64	Specify the base64-encoded secret used to sign the JWT token for HMAC with SHA2 (e.g. HS256) signing algorithms	no	client_options.secret	"bXlzZWNyZXQ=\n"
logout_path	Log out is only triggered when the request path ends on this path	no	'/logout'	‘/sign_out’
acr_values	Authentication Class Reference (ACR) values to be passed to the authorize_uri to enforce a specific level, see RFC9470	no	nil	"c1 c2" å

Below are options for the client_options hash of the configuration:

Field	Description	Required	Default value
identifier	OAuth2 client_id	yes	nil
secret	OAuth2 client secret	yes	nil
config_endpoint	OIDC configuration endpoint	yes	nil
scheme	http scheme to use	no	https
host	host of the authorization server	no	nil
port	port for the authorization server	no	443
authorization_endpoint	authorize endpoint on the authorization server	no	retrived from config_endpoint
token_endpoint	token endpoint on the authorization server	no	retrived from config_endpoint
userinfo_endpoint	user info endpoint on the authorization server	no	retrived from config_endpoint
jwks_uri	jwks_uri on the authorization server	no	retrived from config_endpoint
end_session_endpoint	url to call to log the user out at the authorization server	no	nil

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/msuliq/omniauth_oidc. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

License

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

Code of Conduct

Everyone interacting in the OmniauthOidc project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.