Although there are various methods for restricting access to documents stored on a World Wide Web (WWW) site1 (a Web site), none of the widely used methods is completely suitable for restricting access to Web applications hosted on an otherwise publicly accessible Web site. A new technique, however, provides a mix of features well suited for restrict- ing Web-site or Web-application access to authorized users, including the following: secure user authentication, tamper- resistant sessions, simple access to user state variables by server-side applications, and clean session terminations. This technique, called message-dependent digests with tickets, or MDDT, maintains secure user sessions by passing single-use nonces (tickets) and message-dependent digests of user credentials back and forth between client and server. Appen- dix 2 provides a working implementation of MDDT with PHP server-side code and JavaScript client-side code.