If any of this sounds like a distant cousin to the ways Microsoft is preparing to provide identity-management services of its own through Windows Azure, you're spot-on. Microsoft's current plan is to offer Active Directory in the cloud and charge $2 per user per month for the privilege of using it. Single sign-on to a slew of SaaS apps, including (oh, irony!) Salesforce, is also part of that deal.
[Update: Microsoft has informed me that "Microsoft is charging $2/user/month for Multi-factor Authentication. All other identity and access management features that Windows Azure Active Directory currently offers are free."]
Clearly, existing Salesforce customers with Active Directory already on premises now have a choice, with their existing Salesforce account providing them with a potentially broader, more powerful set of tools. This isn't to say Microsoft should be counted out, but given how there's arguably a far larger base of Salesforce users than Azure users, Salesforce Identity might well prove to be the far more immediately useful and powerful of the two offerings.
This story, "Salesforce vs. Microsoft: Dueling single sign-ons," was originally published at InfoWorld.com. Get the first word on what the important tech news really means with the InfoWorld Tech Watch blog. For the latest developments in business technology news, follow InfoWorld.com on Twitter.