To enable Automated Sign-On for Mainframe to IBM host applications, the MSS Administrative Server must exchange information with the Digital Certificate Access Server (DCAS) on z/OS (OS/390 V2R10 and later). DCAS works with RACF to obtain PassTickets, which act as time-limited single-use passwords in the automated sign-on process.
DCAS is included with z/OS Communications Server, but is not installed by default. You may wish to verify whether DCAS has already been enabled on the mainframe.
For example, if you have been using the Express Logon Facility (ELF) feature of z/OS, then DCAS may already be enabled; however, other z/OS components (such as the Telnet server or RACF) may need additional configuration.