When we look at authentication and authorization aspects of cloud computing, most discussions today point towards various forms of identity federation and claims-based authentication to facilitate transactions between service end points as well as intermediaries in the cloud. Even though they represent another form of paradigm shift from the self-managed and explicit implementations of user authentication and authorization, they have a much better chance at effectively managing access from the potentially large numbers of online users to an organization's resources.
So that represents using trust-based, identity assertion relationships to connect services in the cloud, but what do we do to authenticate end users to establish their identities? Most user-facing services today still use simple username and password type of knowledge-based authentication, with the exception of some financial institutions which have deployed various forms of secondary authentication (such as site keys, virtual keyboards, shared secret questions, etc.) to make it a bit more difficult for popular phishing attacks.
But identity theft remains one of the most prevalent issues in the cloud, and signs show that the rate and sophistication of attacks are still on the rise. The much publicized DNS poisoning type of flaws disclosed by Dan Kaminsky at the Black Hat conference (and related posts on C|Net News, InformationWeek, Wired, ZDNet, CIO, InfoWorld, PC World, ChannelWeb, etc.) earlier point out how fragile the cloud still is, from a security perspective, even at the network infrastructure level.
Strong User Authentication
Thus the most effective way to ensure users are adequately authenticated when using browsers to access services in the cloud, is to facilitate an additional authentication factor outside of the browser (in addition to username/password). Which is essentially multi-factor authentication, but available options today are rather limited when considering requirements of scalability and usability.
The aspect of designing and implementing effective user authentication, was the focus of my recently published article, "Strong User Authentication On the Web", as part of the 16th edition of the Architecture Journal. The article discussed a few viable options at implementing "strong" user authentication for end users in the cloud (not limited to multi-factor authentication), and an architectural perspective on many of the capabilities that together form a strong authentication system.
Just one of the many ways to compose these capabilities together. As we move towards cloud computing, the line between internal security infrastructure and public cloud-based services will continue to blur.