OmniAuth: Standardized Multi-Provider Authentication

NOTICE: This documentation and code is for OmniAuth 1.0 in which each provider will become its own separate gem. If you're looking for the current released version, please visit OmniAuth 0.3 Stable Branch.

An Introduction

OmniAuth is a libary that standardizes multi-provider authentication for web applications. It was created to be powerful, flexible, and do as little as possible. Any developer can create strategies for OmniAuth that can authenticate users via disparate systems. OmniAuth strategies have been created for everything from Facebook to LDAP.

In order to use OmniAuth in your applications, you will need to leverage one or more strategies. These strategies are generally released individually as RubyGems, and you can see a community maintained list on the wiki for this project.

Adding OmniAuth to Your Application

Each OmniAuth strategy is a Rack Middleware. That means that you can use it the same way that you use any other Rack middleware. For example, to use the built-in Developer strategy in a Sinatra application I might do this:

require 'sinatra'
require 'omniauth'

class MyApplication < Sinatra::Base
  use Rack::Session
  use OmniAuth::Strategies::Developer
end

Because OmniAuth is built for multi-provider authentication, I may want to leave room to run multiple strategies. For this, the built-in OmniAuth::Builder class gives you an easy way to specify multiple strategies. Note that there is no difference between the following code and using each strategy individually as middleware. This is an example that you might put into a Rails initializer at config/initializers/omniauth.rb:

Rails.application.config.middleware.use OmniAuth::Builder do
  provider :developer unless Rails.env.production?
  provider :twitter, ENV['TWITTER_KEY'], ENV['TWITTER_SECRET']
end

You should look to the documentation for each provider you use for specific initialization requirements.

Integrating OmniAuth Into Your Application

OmniAuth is an extremely low-touch library. It is designed to be a black box that you can send your application's users into when you need authentication and then get information back. OmniAuth was intentionally built not to automatically associate with a User model or make assumptions about how many authentication methods you might want to use or what you might want to do with the data once a user has authenticated. This makes OmniAuth incredibly flexible. To use OmniAuth, you need only to redirect users to /auth/:provider, where :provider is the name of the strategy (for example, developer or twitter). From there, OmniAuth will take over and take the user through the necessary steps to authenticate them with the chosen strategy.

Once the user has authenticated, what do you do next? OmniAuth simply sets a special hash called the Authentication Hash on the Rack environment of a request to /auth/:provider/callback. This hash contains as much information about the user as OmniAuth was able to glean from the utilized strategy. You should set up an endpoint in your application that matches to the callback URL and then performs whatever steps are necessary for your application. For example, in a Rails app I would add a line in my routes.rb file like this:

match '/auth/:provider/callback', to: 'sessions#create'

And I might then have a SessionsController with code that looks something like this:

class SessionsController < ApplicationController
  def create
    @user = ̈User.find_or_create_from_auth_hash(auth_hash)
    self.current_user = @user
    redirect_to '/'
  end

  protected

  def auth_hash
    request.env['omniauth.auth']
  end
end

The omniauth.auth key in the environment hash gives me my Authentication Hash which will contain information about the just authenticated user including a unique id, the strategy they just used for authentication, and personal details such as name and email address as available. For an in-depth description of what the authentication hash might contain, see the Auth Hash Schema wiki page.

Note that OmniAuth does not perform any actions beyond setting some environment information on the callback request. It is entirely up to you how you want to implement the particulars of your application's authentication flow.

Resources

The OmniAuth Wiki has actively maintained in-depth documentation for OmniAuth. It should be your first stop if you are wondering about a more in-depth look at OmniAuth, how it works, and how to use it.

License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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