"SORUA - Simple Online Remote User Authentication - is a project aimed at developing a standard API for a very simple, decentralised, remote authentication mechanism for HTTP-based applications."
Vanilla supports the SORUA initiative and will provide an AuthServer interface to Vanilla spaces as soon as the specification is finished. We also plan to provide a UserServer frontend for commenting, however this is scheduled as mid-term goal.
Disclaimer: Andreas Bolka - Vanilla co-developer - is co-author of the SORUA specification.