authenticate to SDL KC 12

I tried connecting to an SDL Knowledge Center 12 instance with the command:

$ishSession = New-IshSession -IshPassword $password -IshUserName $username -WsBaseUrl $url

I got this error:

New-IshSession : WSTrust endpoint not configured: '/InfoShareSTS/issue/wstrust/mixed/username/'

A Fiddler capture of logging in through the web interface shows a POST to /InfoShareSTS/account/signin with the request body:


Is this an abnormal authentication setup or can ISHRemote's New-IshSession command replicate this?