Simon Willison’s Weblog


The point of “Open” in OpenID

24th June 2008

TechCrunch report that Microsoft are accepting OpenID for their new HealthVault site, but with a catch: you can only use OpenIDs from two providers: Trustbearer (who offer two-factor authentication using a hardware token) and Verisign. "Whatever happened to the Open in OpenID?", asks TechCrunch’s Jason Kincaid.

Microsoft’s decision is a beautiful example of the Open in action, and I fully support it.

You have to remember that behind the excitement and marketing OpenID is a protocol, just like SMTP or HTTP. All OpenID actually provides is a mechanism for asserting ownership over a URL and then “proving” that assertion. We can build a pyramid of interesting things on top of this, but that assertion is really all OpenID gives us (well, that and a globally unique identifier). In internet theory terms, it’s a dumb network: the protocol just concentrates on passing assertions around; it’s up to the endpoints to set policies and invent interesting applications.

Open means that providers and consumers are free to use the protocol in whatever way they wish. If they want to only accept OpenID from a trusted subset of providers, they can go ahead. If they only want to pass OpenID details around behind the corporate firewall (great for gluing together an SSO network from open-source components) they can knock themselves out. Just like SMTP or HTTP, the protocol does not imply any rules about where or how it should be used.

HealthVault have clearly made this decision due to security concerns—not over the OpenID protocol itself, but the providers that their users might choose to trust. By accepting OpenID on your site you are outsourcing the security of your users to an unknown third party, and you can’t guarantee that your users picked a good home for their OpenID. If you’re a bank or a healthcare provider that’s not a risk you want to take; whitelisting providers that you have audited for security means you don’t have to rule out OpenID entirely.

I have a very simple rule of thumb for whether or not a site should consider whitelisting OpenID providers: does the site offer a “forgotten password” feature that e-mails the user a login token? If it does, then the owners have already made the decision to outsource the security of their users to whoever they picked as an e-mail provider. If they don’t (banks are a good example here) they should continue that policy decision and consider using an OpenID provider whitelist.

I’ve been using the example of banks potentially accepting OpenID only from security audited providers in my talks on OpenID for at least the past year. Now I can finally provide a real-world example.