Login with only kerberos as idp (environment variable) seems broken

Steps to reproduce

1. Install Nextcloud
2. Install user_saml and chose environment variable
3. try to enter REOTE_USER

Expected behaviour

Tell us what should happen
It should take the variable and use it to enable login against kerberos

Actual behaviour

Tell us what happens instead
kerberos authorizes the login, user_saml seems to not catch the value of REMOTE_USER and prints an empty Error page (Nextcloud Errorpage but only Error as Error message
In the error log i can see that kerberos grants the login and in the nextcloudlog i get an error when Nextcloud tries to get the token

Server configuration

Operating system: Ubuntu 20.04

Web server: Apach2

Database: mysql

PHP version: 7.4-cgi

Nextcloud version: (see Nextcloud admin page) 24.x

Where did you install Nextcloud from:
webinstaller

List of activated apps:

  - bbb: 2.4.0
  - cloud_federation_api: 1.7.0
  - dav: 1.22.0
  - federatedfilesharing: 1.14.0
  - files: 1.19.0
  - files_rightclick: 1.3.0
  - files_versions: 1.17.0
  - group_default_quota: 0.1.4
  - lookup_server_connector: 1.12.0
  - nextcloud_announcements: 1.13.0
  - notifications: 2.12.1
  - oauth2: 1.12.0
  - password_policy: 1.14.0
  - privacy: 1.8.0
  - provisioning_api: 1.14.0
  - serverinfo: 1.14.0
  - settings: 1.6.0
  - sharebymail: 1.14.0
  - survey_client: 1.12.0
  - theming: 1.15.0
  - twofactor_backupcodes: 1.13.0
  - updatenotification: 1.14.0
  - user_saml: 5.0.3
  - viewer: 1.8.0
  - workflowengine: 2.6.0

Nextcloud configuration:

[owncloud][PHP][3] {"Exception":"Error","Message":"Array to string conversion at /var/www/nextcloud/lib/private/Log/Errorlog.php#46","Code":0,"Trace":[{"file":"/var/www/nextcloud/lib/private/Log/Errorlog.php","line":46,"function":"onError","class":"OC\\Log\\ErrorHandler","type":"::"},{"file":"/var/www/nextcloud/lib/private/Log.php","line":375,"function":"write","class":"OC\\Log\\Errorlog","type":"->"},{"file":"/var/www/nextcloud/lib/private/Log.php","line":215,"function":"writeLog","class":"OC\\Log","type":"->"},{"file":"/var/www/nextcloud/lib/private/Log.php","line":193,"function":"log","class":"OC\\Log","type":"->"},{"file":"/var/www/nextcloud/lib/private/legacy/OC_App.php","line":183,"function":"debug","class":"OC\\Log","type":"->"},{"file":"/var/www/nextcloud/lib/private/legacy/OC_App.php","line":140,"function":"loadApp","class":"OC_App","type":"::"},{"file":"/var/www/nextcloud/lib/private/Console/Application.php","line":119,"function":"loadApps","class":"OC_App","type":"::"},{"file":"/var/www/nextcloud/console.php","line":99,"function":"loadCommands","class":"OC\\Console\\Application","type":"->"},{"file":"/var/www/nextcloud/occ","line":11,"args":["/var/www/nextcloud/console.php"],"function":"require_once"}],"File":"/var/www/nextcloud/lib/private/Log/ErrorHandler.php","Line":92,"CustomMessage":"--"}
[owncloud][user_saml][0] Array

{
    "system": {
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "cloud.domain.tld",
            "cloud",
            "***REMOVED SENSITIVE VALUE***"
        ],
        "default_phone_region": "DE",
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "24.0.7.1",
        "overwrite.cli.url": "https:\/\/cloud.domain.tld",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "mysql.utf8mb4": true,
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "memcache.local": "\\OC\\Memcache\\APCu",
        "filelocking.enabled": true,
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "memcache.distributed": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "port": 0,
            "timeout": 0
        },
        "maintenance": false,
        "mail_smtpmode": "smtp",
        "mail_smtpauthtype": "LOGIN",
        "mail_sendmailmode": "smtp",
        "mail_smtpauth": 1,
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpport": "587",
        "mail_smtpsecure": "tls",
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***",
        "theme": "",
        "loglevel": 0,
        "log_type": "errorlog",
        "app_install_overwrite": [
            "user_saml"
        ],
        "updater.secret": "***REMOVED SENSITIVE VALUE***"
    }
}

Client configuration

Browser:
Chrome mobile on android
Firefox on Ubuntu 22.04
Operating system:

Logs

Nextcloud log (data/owncloud.log)

Insert your Nextcloud log here

[Thu Nov 17 07:48:05.351829 2022] [php7:notice] [pid 637249] [client **********:43448] [owncloud][user_saml][0] Array
[Thu Nov 17 07:48:05.364705 2022] [php7:notice] [pid 637249] [client **********:43448] [owncloud][no app in context][0] {"Exception":"OC\\\\Authentication\\\\Exceptions\\\\InvalidTokenException","Message":"Token does not exist: token does not exist","Code":0,"Trace":[{"file":"/var/www/nextcloud/lib/private/Authentication/Token/Manager.php","line":133,"function":"getToken","class":"OC\\\\Authentication\\\\Token\\\\PublicKeyTokenProvider","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/nextcloud/lib/private/User/Session.php","line":523,"function":"getToken","class":"OC\\\\Authentication\\\\Token\\\\Manager","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/nextcloud/lib/private/User/Session.php","line":436,"function":"isTokenPassword","class":"OC\\\\User\\\\Session","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/nextcloud/lib/private/User/Session.php","line":575,"function":"logClientIn","class":"OC\\\\User\\\\Session","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/nextcloud/lib/base.php","line":1081,"function":"tryBasicAuthLogin","class":"OC\\\\User\\\\Session","type":"->"},{"file":"/var/www/nextcloud/lib/base.php","line":1019,"function":"handleLogin","class":"OC","type":"::"},{"file":"/var/www/nextcloud/index.php","line":36,"function":"handleRequest","class":"OC","type":"::"}],"File":"/var/www/nextcloud/lib/private/Authentication/Token/PublicKeyTokenProvider.php","Line":115,"Previous":{"Exception":"OCP\\\\AppFramework\\\\Db\\\\DoesNotExistException","Message":"token does not exist","Code":0,"Trace":[{"file":"/var/www/nextcloud/lib/private/Authentication/Token/PublicKeyTokenProvider.php","line":111,"function":"getToken","class":"OC\\\\Authentication\\\\Token\\\\PublicKeyTokenMapper","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/nextcloud/lib/private/Authentication/Token/Manager.php","line":133,"function":"getToken","class":"OC\\\\Authentication\\\\Token\\\\PublicKeyTokenProvider","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/nextcloud/lib/private/User/Session.php","line":523,"function":"getToken","class":"OC\\\\Authentication\\\\Token\\\\Manager","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/nextcloud/lib/private/User/Session.php","line":436,"function":"isTokenPassword","class":"OC\\\\User\\\\Session","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/nextcloud/lib/private/User/Session.php","line":575,"function":"logClientIn","class":"OC\\\\User\\\\Session","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/nextcloud/lib/base.php","line":1081,"function":"tryBasicAuthLogin","class":"OC\\\\User\\\\Session","type":"->"},{"file":"/var/www/nextcloud/lib/base.php","line":1019,"function":"handleLogin","class":"OC","type":"::"},{"file":"/var/www/nextcloud/index.php","line":36,"function":"handleRequest","class":"OC","type":"::"}],"File":"/var/www/nextcloud/lib/private/Authentication/Token/PublicKeyTokenMapper.php","Line":89},"message":"Token is not valid: Token does not exist: token does not exist","exception":{},"CustomMessage":"Token is not valid: Token does not exist: token does not exist"}

Browser log

Insert your browser log here, this could for example include:

a) The javascript console log
b) The network log
c) ...

Start by reproducing the environment-variable IdP flow described for user_saml 5.0.3, then read the referenced authentication paths in lib/base.php, lib/private/User/Session.php, and lib/private/Authentication/Token/. Done means REMOTE_USER is consumed during Kerberos login and the request no longer ends with an empty error page or token failure.