Using network-based security services such as unified login allows you to authenticate with a security mechanism offered by a third-party provider and then log in to SAP ASE without specifying a login name or a password.
Use the -V option of isql to specify network-based user authentication such as unified login.
See isql in the Utility Guide and, External Authentication, in the Security Administration Guide for more information about the options you can specify to use network-based security.