Created attachment 193660 [details]
Diagnostics command outputs:

KRDP System Users authentication fails with PAM/unix_chkpwd, while Other Users works with the same Windows RDP client

DESCRIPTION
On Arch Linux KDE Plasma Wayland, KRDP works correctly when using an account created under “Other Users” in the Remote Desktop KCM. Manual password entry and saved Windows TERMSRV credentials both work for that Other User account.

However, “System Users” authentication for my Linux user fails consistently with the same RDP client. The client reaches the KRDP server, but authentication fails through PAM/unix_chkpwd. This happens even when the correct Linux password is entered manually, and also when the credential is saved using Windows Credential Manager / cmdkey.

STEPS TO REPRODUCE
1. Log into a KDE Plasma Wayland session.
2. Open System Settings → Remote Desktop.
3. Enable KRDP.
4. Test case A: create an “Other Users” account, for example username RDP, and set a password.
5. Connect from Windows using mstsc.exe with username RDP.
6. The connection succeeds.
7. Save the credential in Windows Credential Manager, for example using cmdkey /generic:TERMSRV/<host> /user:RDP /pass:<password>.
8. Connect again using the saved credential.
9. The connection still succeeds.
10. Test case B: enable/use “System Users” for the existing Linux user doge.
11. Connect from the same Windows mstsc.exe client using username doge and the correct Linux login password.
12. The connection fails.
13. Test case C: save the system-user credential manually with cmdkey /generic:TERMSRV/<host> /user:doge /pass:<linux-password>.
14. Connect again.
15. The connection still fails.

OBSERVED RESULT
* KRDP works with Other Users.
* KRDP also works with saved Windows TERMSRV credentials when the credential is for the Other Users account.
* KRDP fails with System Users / Linux user authentication.
* The failure appears in the logs as PAM/unix_chkpwd authentication failure.

Relevant log excerpts:
krdpserver: New client connected: Windows platform Windows NT
unix_chkpwd: check pass; user unknown
unix_chkpwd: password check failed for user (doge)
krdpserver: pam_unix(login:auth): authentication failure; logname=doge uid=1000 euid=1000 tty= ruser= rhost= user=doge
krdpserver: pam_authenticate failure: Authentication service cannot retrieve authentication info
krdpserver: [ERROR][com.freerdp.api] - [rdp_peer_handle_state_active]: PostConnect for peer ... failed


EXPECTED RESULT
System Users authentication should accept the same Linux username and password that work locally for login/sudo, or it should report a clearer error if System Users authentication is unsupported or misconfigured. The behavior should not differ in this way from Other Users unless there is a documented limitation.

SOFTWARE/OS VERSIONS
Operating System (available in the Info Center app, or by running `kinfo` in a terminal window):Arch Linux
KDE Plasma Version: 6.7.1
KDE Frameworks Version: 6.27.0
Qt Version: 6.11.1


Environment:

* Distribution: Arch Linux
* Session: KDE Plasma Wayland
* Hostname: LAPTOP-arch
* Linux user: doge
* RDP client: Windows built-in Remote Desktop Connection / mstsc.exe
* KRDP version: 6.7.1-1
* FreeRDP version: 3.27.1-1
* plasma-workspace: 6.7.1-1
* kwin: 6.7.1-1
* xdg-desktop-portal: 1.22.1-2
* xdg-desktop-portal-kde: 6.7.1-1
* kpipewire: 6.7.1-1
* pipewire: 1.6.7-1
* wireplumber: 0.5.15-1
* qt6-base: 6.11.1-1
* RemoteDesktop portal AvailableDeviceTypes: u 7

ADDITIONAL INFORMATION
* RemoteDesktop Portal itself appears available: AvailableDeviceTypes returns u 7.
* Other Users mode proves that KRDP, the Windows RDP client, PipeWire, and the RemoteDesktop portal are basically functional.
* The issue seems isolated to the System Users / PAM authentication path.
* After a clean KRDP reinstall, KRDP also logs:

Failed to register with host portal QDBusError("org.freedesktop.portal.Error.Failed", "Could not register app ID: App info not found for 'org.kde.krdp-server'")

This may be a separate packaging/app-id issue, but I am including it in case it is related.

Workaround:
Use an account created under Remote Desktop → Other Users instead of System Users.