For basic authorization, if you use a browser to access the site, you will get a popup window, above the user/password entry fields is the name of the realm. For example, if you access: http://www.zoneedit.com/auth/, you will see the realm is "ZoneEdit Access". Of course, you can also inspect the headers by, say, "wget -S http://www.zonedit.com/auth/", you will see a line:

WWW-Authenticate: Basic realm="ZoneEdit Access"