On the login page, open the server behaviors panel. double click the security assist authenticate user server behavior to edit it (there may be 2, one for the login form, another for auto login, if you have 2, you instances, you will need to edit both).
on the sessions tab, click the plus button and select the username column to save the username to a session.
on the page you would like to show the username, open the bindings panel, expand the session section and add the username session binding where you would like to show the username.