You have been asked to find an authentication service that is handled by a third party. The service should allow users to access multiple websites, as long as they support the third-party authentication service. What would be your best choice?

The right answer is that OpenID is an authentication service often done by a third party, and it can be used to sign into any website that accepts OpenID. Kerberos is a network authentication protocol for use within a domain. New Technology LAN Manager (NTLM) is an older Windows authentication protocol. Shibboleth is a single sign-on system, but it works with federated systems.