It was VMWare VCentre/VSphere end to end for all private clients.
There were some great GUIs and great management but if you wanted serious API access it was the one of the most hacked up thing I have ever seen in my career.
Pay a sysadmin to be up at night, then before your job is meant to run, have them log into the VSphere GUI, open devtools, click refresh to trigger a GET request, copy the cookie, paste the cookie into our custom software, and send it in the cookies of our API requests.
When we asked if there was an easier way, they said that we could probably use Selenium to automate that.
Needless to say, we did not sign the contract, and moved wholesale into AWS.
Not funny. :)
API access got a lot better once they introduced the powershell API (which can also be used via C#) but the solution you're describing is the result of people not knowing what they're doing.
I stopped using it in like 2014 or 2015 after years of requesting improvements (like better ways to automate things without stuff breaking all the time).
It sounds great they have arrived at the 20th century. Powershell and C#? Don't tell me it is SOAP and all XML? I kinda like the way most cloud apis are just REST and json under the hood with vendor supported python packages that work well on all major platforms.