OpenID holds much promise as a means of supporting a single digital identity that can be used across the Internet. Currently there are several types of OpenID identity providers out there, and several of the major players on the web, including AOL, Microsoft, Google, and Yahoo!, have committed to become OpenID providers as well. While there is some concern about the 'Balkanization' of OpenID by these service providers (essentially the concern is over the fact that service providers will only provide OpenIDs and subsequently they will not become consumers of OpenIDs from other providers), the positive side of this adoption is that hundreds of millions of existing user accounts can now be used as OpenIDs.
However, there is one catch: at present implementing OpenID support for more than one of these providers can be challenging, given that the OpenID specifications and extensions supported vary among each provider. Enter RPX, a new software as a service (SaaS) that handles the user interface, authentication, and import of user profile and registration data for any web site.
RPX essentially serves as a proxy that utilizes OpenID (and several other open standards such as OAuth and HCard) to provide users on your web site with the ability to register and sign in using several different accounts, including AOL, Facebook, Google, MySpace, Yahoo!, and many other OpenID providers. Rather than trying to figure out which provider supports which specification and extension, RPX presents a unified sign in form that allows your site to become an OpenID consumer that supports accounts from the major service providers.
According to the RPX web site:
When a visitor is ready to sign in or register at your website, you display the provided RPX login interface. The sign-in interface helps the user choose their provider, and then RPX authenticates the user with their provider. The sign-in interface can be added as a popup overlay, or embedded directly into your webpage. If you’d like to build your own custom interface, that is also possible.
RPX includes an API that can be used to customize your implementation of the service, including the user interface (see our RPX API profile for details). Currently RPX is available as a freemium service. You can check out the full documentation available on the service and API. RPX was developed by JanRain, an OpenID solutions provider from Portland, Oregon.