Can SSO be implemented on client-server applications?
Yes. Kerberos is an example of a client-server SSO system.
In Web services, Passport and Liberty are SSO solutions designed for what is effectively SSO. Now of course, there have been flaws found in Passport and it took years for Kerberos to be mostly bug-free. This isn't easy. But it's certainly possible.
For more information on this topic, visit these other SearchSecurity resources:
Best Web Links: Authentication
Tech Tip: Kerberos and network access security
Ask the Expert: Factors to consider before implementing SSO