Single Sign On (SSO)
"Intranet users are commonly required to use a separate password to authenticate themselves to each server they need to access in the course of their work. Multiple passwords are an ongoing headache for both users and system administrators. Users have difficulty keeping track of different passwords, tend to choose poor ones, and tend to write them down in obvious places. Administrators must keep track of a separate password database on each server and deal with potential security problems related to the fact that passwords are sent over the network routinely and frequently.
Solving this problem requires some way for a user to log in once, using a single password, and get authenticated access to all servers that user is authorized to use--without sending any passwords over the network. This capability is known as single sign-on."
- SAML is an XML framework for exchanging authentication and authorization information.
- drupal has something.
- wiki page: