CSC/ECE 517 Spring 2015/ch1b 21 QW

Omniauth

Omniauth is a Ruby authentication framework aimed to integrated with various types of authentication providers. It can be hooked up to any system, from social network to enterprise systems to simple username and password authentication. <ref>https://github.com/intridea/omniauth/wiki</ref>

The topic writeup for this page can be found here.

Background

With web application booming, most users login hundreds of services every day and won't expect to create unique login and password for each service. So intridea recently releases a standard library to provide multi-provider authentication for web applications.

Getting Start

Each OmniAuth strategy is a Rack Middleware, which means it can be used the same way as other Rack middleware. Here we introduce some simple steps to illustrate how to use Twitter strategy for OmniAuth.<ref>https://github.com/intridea/omniauth</ref>

Modifying Gemfile

First start by adding this gem to your Gemfile:

gem 'omniauth-twitter'

If you need to use the latest HEAD version, you can do so with:

gem 'omniauth-twitter', :github => 'arunagw/omniauth-twitter'

Building OmniAuth Strategies

Because OmniAuth is built for multi-provider authentication, you need to build multiple strategies. For this, the Rack middleware OmniAuth::Builder class gives an easy way to build up your list of OmniAuth strategies for use in your application.

Below is an example that you can put into a Rails initializer at config/initializers/omniauth.rb or add it to your middleware:

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

Where "TWITTER_KEY" and "TWITTER_SECRET" is the appropriate values you obtained here.

Integrating OmniAuth into Rails Application

OmniAuth is a library extremely easy to use. 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. 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, 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 you can add a line in routes.rb file like this:

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

And in Sinatra, a callback might look something like this:

# Support both GET and POST for callbacks
%w(get post).each do |method|
  send(method, "/auth/:provider/callback") do
    env['omniauth.auth'] # => OmniAuth::AuthHash
  end
end

Also of note, by default, if user authentication fails on the provider side, OmniAuth will catch the response and then redirect the request to the path /auth/failure, passing a corresponding error message in a parameter named message. You may want to add an action to catch these cases. Continuing with the previous Sinatra example, you could add an action like this:

get '/auth/failure' do
  flash[:notice] = params[:message] # if using sinatra-flash or rack-flash
  redirect '/'
end

And then have 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 the 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.

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.

Logging

OmniAuth supports a configurable logger. By default, OmniAuth will log to STDOUT but you can configure this using OmniAuth.config.logger:

# Rails application example
OmniAuth.config.logger = Rails.logger

References

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