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'

  provider :facebook,
           SiteSetting.facebook_app_id,
           SiteSetting.facebook_app_secret,
           :scope => "email"

  provider :twitter,
           SiteSetting.twitter_consumer_key,
           SiteSetting.twitter_consumer_secret

end