AllowGroups statement in sshd_config chokes on umlauts and probably other non [a-z0-9] characters

Troubleshooting steps
https://github.com/PowerShell/Win32-OpenSSH/wiki/Troubleshooting-Steps

Terminal issue? please go through wiki
https://github.com/PowerShell/Win32-OpenSSH/wiki/TTY-PTY-support-in-Windows-OpenSSH

No

Please answer the following

"OpenSSH for Windows" version
((Get-Item (Get-Command sshd).Source).VersionInfo.FileVersion)

7.7.2.2

Server OperatingSystem
((Get-ItemProperty "HKLM:\SOFTWARE\Microsoft\Windows nt\CurrentVersion\" -Name ProductName).ProductName)

Windows Server 2019 Datacenter ( 10.0.17763.1339 )

Client OperatingSystem

Windows 10 Pro ( 10.0.19041.388 )

What is failing

Logging in via ssh through a group membership authorization where the group name contains characters like ä.
I tried with another group name that only contains regex [a-z] characters and it worked right away.

Example: AllowGroups domain\käsebrot

Expected output

The prompt of my server

Actual output

Permission denied, please try again.

Start by reproducing the AllowGroups case from the issue, using the example group name domain\käsebrot on the stated OpenSSH for Windows and Windows Server versions. Trace how sshd_config reads and matches group names, then verify that login authorization succeeds for names containing umlauts while preserving the existing behavior for ASCII names.