A system for providing single sign-on (SSO) user names for Web cookies in a multiple user information directory environment. SSO access to multiple applications is supported in situations where multiple user information directories are deployed, and users may be known by multiple identifiers. Convenient specification is enabled for which of a user's multiple names is to be used in an SSO Web cookie that is passed from application to application to enable SSO operation. The user's SSO Web cookie user name is fully separated conceptually from the user's effective name for any given application within the SSO environment. The SSO Web cookie user name provided by the disclosed system is specified independently from the effective name by which the user is known when operating in the Web application that writes the SSO Web cookie back to the user's computer system. Use of an administratively supplied user name in the SSO Web cookie is facilitated.