Chris, assuming it is one of the websites
listed in your post ( excepting the persnet site )
they are all hosted on Apache Servers running UNIX.
Therefore, you need to use .htaccess and .htpasswd
files to do this.
..htaccess lives in the folder you want protected
..htpasswd lives "above" the root of the web.
If you have the Webmasters control panel
named CPanel, you can be able to do it with
the built in Web Protect feature if it's available
Main control pane > Access Menu > Web Protect.
obtw- I was initiated as an AMSC at the
NATTC Millington CPO club in Sept 1979.
If you run across an old beat up retired AFCM
named Mike Taylor ( still lives in Mumford I think )
Tell him I said hello.
( he and another AFCM took my charge book,
doused it with lighter fluid, lit it on fire and chunked it
the front door of the CPO club at lunchtime.
1 week before my initiation. My "fines" were the highest
ever recorded at Millington. )
True Story.
