Issue: SSH login fails for usernames containing uppercase letters (Resolute)

[nooreldeenmansour]

Attempting to log in via SSH using uppercase letters in the username causes an error.

Environment

• Ubuntu 26.04 (Development Branch)
• openssh-server version: 1:10.2p1-2ubuntu1
• authd version: Reproduced on both edge and stable PPA versions
• Note: This issue does not occur on Ubuntu 24.04 LTS.

Steps to reproduce

1. Ensure you have an existing authenticated authd user, for example: test@ubudev1.onmicrosoft.com
2. Attempt to SSH into the account using a capitalized letter in the username:

   ssh Test@ubudev1.onmicrosoft.com@<host>

Expected behavior
The SSH login should succeed.

Actual behavior
The login fails with this error:

Connection closed by <host> port 22

The logs show the following error:

sshd-session[8157]: fatal: PAM user mismatch

The issue doesn't seem to be caused by authd, but since it affects 26.04, I've created this issue to track it here