discourse/config/initializers/omniauth.rb

require "openssl"
require "openid_redis_store"

# if you need to test this and are having ssl issues see:
#  http://stackoverflow.com/questions/6756460/openssl-error-using-omniauth-specified-ssl-path-but-didnt-work

Rails.application.config.middleware.use OmniAuth::Builder do

  provider :open_id,
           :store => OpenID::Store::Redis.new($redis),
           :name => "google",
           :identifier => "https://www.google.com/accounts/o8/id",
           :require => "omniauth-openid"

  provider :open_id,
           :store => OpenID::Store::Redis.new($redis),
           :name => "yahoo",
           :identifier => "https://me.yahoo.com",
           :require => "omniauth-openid"

  Discourse.auth_providers.each do |p|
    if p.type == :open_id
      provider :open_id, {
        :name => p.name,
        :store => OpenID::Store::Redis.new($redis),
        :require => "omniauth-openid"
      }.merge(p.options)
    end
  end

  # lambda is required for proper multisite support,
  #  without it subdomains will not function correctly
  provider :facebook,
           :setup => lambda { |env|
              strategy = env["omniauth.strategy"]
              strategy.options[:client_id] = SiteSetting.facebook_app_id
              strategy.options[:client_secret] = SiteSetting.facebook_app_secret
           },
           :scope => "email"

  provider :twitter,
           :setup => lambda { |env|
              strategy = env["omniauth.strategy"]
              strategy.options[:consumer_key] = SiteSetting.twitter_consumer_key
              strategy.options[:consumer_secret] = SiteSetting.twitter_consumer_secret
           }

  provider :github,
           :setup => lambda { |env|
              strategy = env["omniauth.strategy"]
              strategy.options[:client_id] = SiteSetting.github_client_id
              strategy.options[:client_secret] = SiteSetting.github_client_secret
           },
           :scope => "user:email"

  provider :browser_id,
           :name => "persona"

  provider :cas,
           :host => SiteSetting.cas_hostname

end