Can Stack Overflow implement single sign on for its all sites?

Question

Can Stack Overflow implement single sign on so that users do not have to sign-in again when they visit other Stack Exchange sites like Meta Stack Overflow, Server Fault, Super User, etc.?

Answer 1

With the growth in the number of StackExchange sites the merits of a unified login system are growing as well.

Eventually, logging into StackOverflow will cause you to be logged into, say, Cooking too. All of this is conditioned on you already having an account on both sites.

We've already taken steps in this direction by unifying logins between parent and child-meta sites.

Answer 2

This is now complete; see

https://blog.stackoverflow.com/2010/09/global-network-auto-login/

for details

Answer 3

There are possible reasons why it could not work:

• You’ve been to the target site recently without a global auth session (click the “login” link at the top of every page to force it)
• You’re using some sort of anonymizer that interferes with HTTP Referrer
• You aren’t using the same OpenId across all sites
• You’re visiting a per-site meta without first logging into the parent (child metas don’t use global auth; they rely on identity coming from the parent site.)

Answer 4

That's somewhat the point of OpenID - if you associate an OpenID with your account, then signing into Stack Exchange site with the same OpenID will automatically import and link your account from other sites.