MsRdpEx session connection failed with authentication error

[roman-pr-v]

Environment:

1. sspi-rs: master - c016e18
2. MsRdpEx: v2026.01.12.0 - da020e1 (https://github.com/Devolutions/MsRdpEx/releases)
3. Windows Server: Edition: Windows Server 2025 Standard Evaluation, Version: 24H2, OS build: 26100.32370, Experience: Windows Feature Experience Pack 1000.26100.275.0 [VM]
4. RDP Server: Edition: Windows 11 Pro, Version: 25H2, OS build: 26200.7840, Experience: Windows Feature Experience Pack 1000.26100.291.0 [VM]
5. RDP Client: Edition: Windows 11 Pro, Version: 25H2, OS build: 26200.7840, Experience: Windows Feature Experience Pack 1000.26100.291.0 [VM]

Preconditions:

1. Windows Server 2025 [VM] is configured and launched:

• set up and configure Active Directory
• set up and configure DNS server
• create a user for the domain-joined machine

2. RDP server [VM] is configured and launched:

• join Windows 11 to our domain
• enable Remote Desktop
• grant users access via RDP
• modify hosts file

3. RDP Client [VM] is configured and launched:

• modify hosts file
• install MsRdpEx
• set up environment variables:
  SSPI_KDC_URL -
  SSPI_LOG_LEVEL - trace
  SSPI_LOG_PATH - <path/to/sspi/logfile>
  MSRDPEX_CREDSSP_DLL - <path/to/sspi.dll>
  MSRDPEX_LOG_ENABLED - 1
  MSRDPEX_LOG_FILE_PATH <path/to/msrdpex/logfile>
  MSRDPEX_LOG_LEVEL - TRACE

Steps:

1. Open MsRdpEx app
2. Enter valid destination address (for example: TST-RDPS-NM.negomod.lab.test)
3. Enter valid username (for example: joe-moon)
4. Enter valid password
5. Click Connect button

Actual Result: MsRdpEx session connection failed with authentication error, see log in attach: sspi-negomod.log, msrdpex.logs.txt, msrdpex-authentication-error.png

[sspi-negomod.log](https://github.com/user-attachments/files/25514386/sspi-negomod.log) [msrdpex.logs.txt](https://github.com/user-attachments/files/25514387/msrdpex.logs.txt)

Expected Result: MsRdpEx connection should be established successfully. The user should be granted access to the system, and the system should proceed to the user's desktop. You can see the remote screen.

NOTE:

1. Issue also reproduced with FQDN username format, for example: joe-moon@negomod.lab.test
2. Issue not reproduced with FreeRDP client, checked with FreeRDP (master - 934a486)

[RRRadicalEdward]

Hi roman-pr-v. Logs didn't get attached