Bug#955541: Login fails for a user name with non-ascii characters

[Sam Morris]

Package: systemd
Followup-For: Bug #955541
Control: affects -1 + sssd

This also prevents logging in using Active Directory credentials with
sssd. This is because sssd synthesizes an AD user's user name with:

CONCAT(SAM-Account-Name, '@', DNS Domain Name)

This also applies to group names.

It's worth remarking that a user or group SAM-Account-Name can contain
other characters that systemd isn't happy about such as commas and
spaces.

-- Package-specific info:

-- System Information:
Debian Release: 10.3
  APT prefers stable-debug
  APT policy: (570, 'stable-debug'), (570, 'stable'), (550, 'testing-debug'), (550, 'testing'), (530, 'unstable-debug'), (530, 'unstable'), (500, 'stable-updates'), (1, 'experimental-debug'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 5.4.0-4-amd64 (SMP w/4 CPU cores)
Kernel taint flags: TAINT_USER, TAINT_WARN
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB:en (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: SELinux: enabled - Mode: Permissive - Policy name: default

Versions of packages systemd depends on:
ii  adduser          3.118
ii  libacl1          2.2.53-4
ii  libapparmor1     2.13.2-10
ii  libaudit1        1:2.8.4-3
ii  libblkid1        2.33.1-0.1
ii  libc6            2.30-2
ii  libcap2          1:2.25-2
ii  libcrypt1        1:4.4.15-1
ii  libcryptsetup12  2:2.1.0-5+deb10u2
ii  libgcrypt20      1.8.4-5
ii  libgnutls30      3.6.12-2
ii  libgpg-error0    1.35-1
ii  libidn2-0        2.0.5-1+deb10u1
ii  libip4tc2        1.8.3-2~bpo10+1
ii  libkmod2         26-1
ii  liblz4-1         1.8.3-1
ii  liblzma5         5.2.4-1
ii  libmount1        2.34-0.1
ii  libpam0g         1.3.1-5
ii  libpcre2-8-0     10.34-7
ii  libseccomp2      2.4.3-1
ii  libselinux1      3.0-2.1
ii  libsystemd0      245.2-1.1
ii  mount            2.34-0.1
ii  util-linux       2.34-0.1

Versions of packages systemd recommends:
ii  dbus  1.12.16-1

Versions of packages systemd suggests:
ii  policykit-1        0.105-25
pn  systemd-container  <none>

Versions of packages systemd is related to:
pn  dracut           <none>
ii  initramfs-tools  0.133+deb10u1
ii  libnss-systemd   245.2-1.1
hi  libpam-systemd   245.2-1.1
ii  udev             244.3-1

-- Configuration Files:
/etc/pam.d/systemd-user changed [not included]

-- no debconf information