Currently for the various identity providers, DataUp uses the Windows Azure Identity Services. Not only is the functionality for Azure identity services pretty complex but it's not free for others to use. ASP.Net Web Pages has built in support for various OAuth services in the Microsoft.Web.WebPages.OAuth assembly. It's simple to use and free to other people who want to create DataUp style web sites.
NOTE: Each site requires some sort of access token for your use of the service. DataUp's access token should be in an Web.config or App.config file and then encrypted so users can't make calls on behalf of the official DataUp service.