You see this page of the Add Server Instance wizard when you specify domain details to register an instance of the Sun Java System Application Server/Glassfish. Use this page of the wizard to specify the username and password to use to login as domain administrator.
You are not required to supply a domain admin username and password when registering a server instance. If you do not supply a username and password when registering an instance, you are prompted to supply a username and password when needed.
In this page of the wizard you can supply the following information: