— Thanks so much for your contribution! I couldn't have figured it out without your post.
However, I wanted to elaborate on your approach because I had to get past some wrong assumptions on my part to get it working, and thought what I learned might help others.
First. be sure to URL encode the username:password.
In my case the username was an email address with an @-sign, and the password had a #-sign, so if my username and password were foo@bar.com and #elloWorld then my URL-encoded version would be foo%40bar.com%3A%23elloWorld.
You can google for a URL encoder, or just use urlencoder.org.
Also, I had a mental block about https://ESXI_HOSTNAME/folder. I never actually went to that URL but instead tried to find the link in the vSphere UI.
So... if you are reading this be sure to visit just the https://ESXI_HOSTNAME/folder URL with nothing after it — of course replacing ESXI_HOSTNAME with your site's IP address or domain name — and then I think everything else should become clear.
Hope this helps.
P.S. OTOH it would be MUCH nicer if VMware just added this functionality to the menu in the UI...