I want to view a web application screen of the SMARTDAC+ GX/GP with the enhanced security option (/AS), but I can't log in. In the hardware configurator, I was able to log in with an administrator user name and password and perform communication.

Only monitor users can log in to the web application of the enhanced security function. Administrators and general users cannot. To log in to the web application screen, register a monitor user.
See section 1.3.3, "User Levels" in IM 04L51B01-05EN.