To simply append a string to the gateway username, configure the append_domain parameter. In this case, SPS automatically appends the @ character and the value of this option to the username from the session, and uses the resulting username on the Starling server to authenticate the user. For example, if the domain is set as append_domain: example.com and the username is Example.User, the SPS plugin will look for the user Example.User@example.com on the Starling server.