The Config API Client sample works with basic authentication users the same way as it does for Windows/AD users.
Please note that the user must have the proper rights, try first with a user in the Administrators role.
I did the test.
I used the Admin Tab plugin sample to make sure I had a custom property.
With the sample plugin deployed I opened the Management Client and added properties.
I then opened the Config API Client sample and logged in with my basic admin user, I then found:
