Disabled users throw constant fatal frror in logs: `ServiceUnavailable` + `LoginException`

I deactivated a user on my installation and this is also the only deactivated user. Apparently a device of said user is still configured to sync and therefore tries to log in. The server log shows fatal errors. If this is standard behaviour, I think that is a bug. Deactivating a user is a standard procedure. Hence a login attempt is not an error. Maybe it justifies some debug / ingo logging, but not to throw an exception.

(And the german "Benutzer deaktiviert" does not belong there either. ^^)

[webdav] Fatal: Sabre\DAV\Exception\ServiceUnavailable: OC\User\LoginException: Benutzer deaktiviert at <<closure>>

0. /var/www/virtual/eppcloud/html/3rdparty/sabre/dav/lib/DAV/Auth/Plugin.php line 193
   OCA\DAV\Connector\Sabre\Auth->check(Sabre\HTTP\Request {}, Sabre\HTTP\Response {})
1. /var/www/virtual/eppcloud/html/3rdparty/sabre/dav/lib/DAV/Auth/Plugin.php line 144
   Sabre\DAV\Auth\Plugin->check(Sabre\HTTP\Request {}, Sabre\HTTP\Response {})
2. /var/www/virtual/eppcloud/html/3rdparty/sabre/event/lib/WildcardEmitterTrait.php line 89
   Sabre\DAV\Auth\Plugin->beforeMethod(Sabre\HTTP\Request {}, Sabre\HTTP\Response {})
3. /var/www/virtual/eppcloud/html/3rdparty/sabre/dav/lib/DAV/Server.php line 458
   Sabre\DAV\Server->emit("beforeMethod:PROPFIND", [Sabre\HTTP\Requ ... }])
4. /var/www/virtual/eppcloud/html/3rdparty/sabre/dav/lib/DAV/Server.php line 251
   Sabre\DAV\Server->invokeMethod(Sabre\HTTP\Request {}, Sabre\HTTP\Response {})
5. /var/www/virtual/eppcloud/html/3rdparty/sabre/dav/lib/DAV/Server.php line 319
   Sabre\DAV\Server->start()
6. /var/www/virtual/eppcloud/html/apps/dav/lib/Server.php line 320
   Sabre\DAV\Server->exec()
7. /var/www/virtual/eppcloud/html/apps/dav/appinfo/v2/remote.php line 35
   OCA\DAV\Server->exec()
8. /var/www/virtual/eppcloud/html/remote.php line 167
   require_once("/var/www/virtua ... p")

PROPFIND /remote.php/dav/principals/users/[deactivated-user]/
from 2a01:c23:7c4f:8400:5415:34a9:5636:47ed at 2020-09-09T20:49:48+00:00

[no app in context] Error: OC\User\LoginException: Benutzer deaktiviert at <<closure>>

 0. /var/www/virtual/eppcloud/html/lib/private/User/Session.php line 617
    OC\User\Session->completeLogin("*** sensitive parameters replaced ***")
 1. /var/www/virtual/eppcloud/html/lib/private/User/Session.php line 366
    OC\User\Session->loginWithPassword("*** sensitive parameters replaced ***")
 2. /var/www/virtual/eppcloud/html/lib/private/User/Session.php line 459
    OC\User\Session->login("*** sensitive parameters replaced ***")
 3. /var/www/virtual/eppcloud/html/apps/dav/lib/Connector/Sabre/Auth.php line 131
    OC\User\Session->logClientIn("*** sensitive parameters replaced ***")
 4. /var/www/virtual/eppcloud/html/3rdparty/sabre/dav/lib/DAV/Auth/Backend/AbstractBasic.php line 106
    OCA\DAV\Connector\Sabre\Auth->validateUserPass("*** sensitive parameters replaced ***")
 5. /var/www/virtual/eppcloud/html/apps/dav/lib/Connector/Sabre/Auth.php line 254
    Sabre\DAV\Auth\Backend\AbstractBasic->check(Sabre\HTTP\Request {}, Sabre\HTTP\Response {})
 6. /var/www/virtual/eppcloud/html/apps/dav/lib/Connector/Sabre/Auth.php line 156
    OCA\DAV\Connector\Sabre\Auth->auth(Sabre\HTTP\Request {}, Sabre\HTTP\Response {})
 7. /var/www/virtual/eppcloud/html/3rdparty/sabre/dav/lib/DAV/Auth/Plugin.php line 193
    OCA\DAV\Connector\Sabre\Auth->check(Sabre\HTTP\Request {}, Sabre\HTTP\Response {})
 8. /var/www/virtual/eppcloud/html/3rdparty/sabre/dav/lib/DAV/Auth/Plugin.php line 144
    Sabre\DAV\Auth\Plugin->check(Sabre\HTTP\Request {}, Sabre\HTTP\Response {})
 9. /var/www/virtual/eppcloud/html/3rdparty/sabre/event/lib/WildcardEmitterTrait.php line 89
    Sabre\DAV\Auth\Plugin->beforeMethod(Sabre\HTTP\Request {}, Sabre\HTTP\Response {})
10. /var/www/virtual/eppcloud/html/3rdparty/sabre/dav/lib/DAV/Server.php line 458
    Sabre\DAV\Server->emit("beforeMethod:PROPFIND", [Sabre\HTTP\Requ ... }])
11. /var/www/virtual/eppcloud/html/3rdparty/sabre/dav/lib/DAV/Server.php line 251
    Sabre\DAV\Server->invokeMethod(Sabre\HTTP\Request {}, Sabre\HTTP\Response {})
12. /var/www/virtual/eppcloud/html/3rdparty/sabre/dav/lib/DAV/Server.php line 319
    Sabre\DAV\Server->start()
13. /var/www/virtual/eppcloud/html/apps/dav/lib/Server.php line 320
    Sabre\DAV\Server->exec()
14. /var/www/virtual/eppcloud/html/apps/dav/appinfo/v2/remote.php line 35
    OCA\DAV\Server->exec()
15. /var/www/virtual/eppcloud/html/remote.php line 167
    require_once("/var/www/virtua ... p")

PROPFIND /remote.php/dav/principals/users/[deactivated-user]/
from 2a01:c23:7c4f:8400:5415:34a9:5636:47ed at 2020-09-09T20:49:48+00:00

Server configuration detail

Operating system: Linux 2.6.32-754.15.3.el6.x86_64 #1 SMP Tue Jun 18 16:25:32 UTC 2019 x86_64

Webserver: Apache/2.2.15 (CentOS) (cgi-fcgi)

Database: mysql 5.1.73

PHP version: 7.2.31

Modules loaded: Core, date, libxml, openssl, pcre, sqlite3, zlib, bcmath, bz2, calendar, ctype, curl, dom, hash, fileinfo, filter, ftp, gd, gettext, gmp, SPL, iconv, session, intl, json, ldap, mbstring, standard, mysqlnd, pcntl, mysqli, PDO, pdo_mysql, pdo_pgsql, pdo_sqlite, pgsql, Phar, posix, pspell, Reflection, imap, shmop, SimpleXML, soap, sockets, exif, sysvmsg, sysvsem, sysvshm, tidy, tokenizer, xml, xmlreader, xmlrpc, xmlwriter, xsl, zip, cgi-fcgi, redis, imagick, Zend OPcache

Nextcloud version: 19.0.2 - 19.0.2.2

Updated from an older Nextcloud/ownCloud or fresh install: updated

Where did you install Nextcloud from: updater

External storages: yes

Encryption: no

User-backends:

OC\User\Database

Start with apps/dav/lib/Connector/Sabre/Auth.php and lib/private/User/Session.php, then reproduce the DAV PROPFIND request using a deactivated user's credentials. Trace how the disabled-user LoginException becomes a fatal ServiceUnavailable log entry. Done means the expected authentication response remains intact without repeated fatal errors or the German exception text in server logs.