I'm using a single sign-on (SSO) solution called TAM (Tivoli Access Manager) Webseal for my authentication.
Basically, when a user goes to my site through TAM they sign on using our web form. I don't want them to have to re-sign on to WordPress. I need it to pass the user credentials to WordPress, and automatically create a user account for the person and log them in. Aka, single sign on.
TAM uses the HTTP_IV_USER variable. User credentials are passed through the headers.