Hi Tuanphan,
Thanks for getting back to me.
I ended up putting that external link into a password protected page on the site. It's adds an extra click than if the external link was directly in the menu / navigation and was password protected on it's own, but it works fine and gives my client the option to include extra info / instructions on that page at some point in the future if needed. Swithenbank Construction
password protected page = files
Still curious if it's actually possible to simply drop a password onto the external link directly and then have it open to the external site / page, but definitely not urgent at this point.
Thanks again for getting back to me.
Cheers,
Anthony