How to revoke OpenID access authorizations?

Which 3rd parties' access do you want to revoke? And why (if you don't mind me asking)?

I don't have any right now, but the fact that there doesn't seem to be a feature to do so seems like a security problem to me and makes me nervous about using launchpad as an openID provider. Others seem to provide such a way to revoke authorizations from a central place.

Example:
https://www.google.com/accounts/IssuedAuthSubTokens?service=profiles

Those other services (including the one you've pointed to) are using OAuth, not OpenID. With OpenID there's not need for that because each time you log into the service the server needs to contact the OpenID provider to authenticate the access.

As for revoking OAuth tokens, you can do that from your https://login.ubuntu.com/+applications page.

The only time the ability to revoke access is needed in OpenID is if the provider provides auto-authorisation functionality so that you don't get prompted every time you want to log in to a site. Ubuntu SSO doesn't currently support that so what you're asking for isn't needed yet. When we do bug #600583 ("Enable user-controlled auto-login"), the ability to revoke auto-authorisation per-site will be added (see the bug's description for more details).