Question: I tried to log-in with my OpenID provider, the log-in screen says: "Unable to log in with your OpenID provider: No OpenID endpoint found." And indeed, it appears my OpenID provider is no longer operating. What do I do?
StackExchange sites use OpenID to verify your identity. You can choose to use one of the many OpenID providers when you first sign-up for an account (you may already be a member of a service that provides OpenID service, such as Google, Facebook, and Wordpress.com, to name a few that is supported on our log-in interface).
OpenID offers a unified authentication platform which makes it easier on users: you only need to remember the log-in for one particular website and reduces password security risks, and it makes it easier to control the sharing of your private information.
On the other hand, separating the authentication from StackExchange does mean that it is possible for problems on third party websites to lock you out of your account. Yes, it has happened before.