I notice that there is an oAuth endpoint for the stackexchange API: https://api.stackexchange.com/docs/authentication

The OpenID implementation used by StackExchange is open sourced at https://code.google.com/p/stackid/

Is there an open source implementation of the oAuth2 provider capabilities used by stackexchange API? If not, any information on what (C#?) implementation the stackexchange network uses?