The present invention provides methods, systems, computer program products, and methods of doing business whereby legacy host application/system access is integrated with single sign-on in a modem distributed computing environment. A security token used for signing on to the modem computing environment is leveraged, and is mapped to user credentials for the legacy host environment. These user credentials are programmatically inserted into a legacy host data stream, thereby giving the end user the look and feel of seamless access to all applications/systems, including not only modem computing applications/systems but also those residing on (or accessible through) legacy hosts. In addition to providing users with the advantages of single sign-on, the disclosed techniques enable limiting the number of user identifiers and passwords an enterprise has to manage.