The default username is "admin" with a blank password.
I suspect that what you are running into is that you are accessing the
admin console from a different host from where the GlassFish server is
running. The security check is failing because secure admin is not
enabled. By default, you can only access the admin console from localhost.
Try:
asadmin enable-secure-admin
asadmin restart-domain
and then try to access the admin console.
Tom