[Nut-upsuser] Which credentials are used to logon to the upsset.cgi page?

[Richard]

  Whenever I try to set a value like battery.charge.low using the 
Network UPS Tools upsset 2.4.3 cgi script, I get an error:  Unexpected 
response: ERR ACCESS-DENIED

I can not start a quick UPS test either.

Which credentials are used to logon to the upsset.cgi page?  I've tried...

the username that I configured in upsd.users
the root credentials
adding a POSIX account & password to match the username configured in 
upsd.users
giving the ups monitoring POSIX account a valid shell (now disabled)

Have I misconfigured something or missed something in the docs?  I'm 
getting the UPS statistics fine.