[Bug]: Contact Search: System Address Book Avatar (Image) URL issue with IMAP

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

When searching for a system address book user using the contact search button, the user's image avatar url needs to be escaped when using UserExternal_IMAP authentication.

This is what the system generates, which does not work:
https://my.nextcloud.installation/remote.php/dav/addressbooks/system/system/system/OCA\UserExternal\IMAP:usercard.vcf?photo&size=32

Manually editing the url to escape each '\' to '%5c' does work:
https://my.nextcloud.installation/remote.php/dav/addressbooks/system/system/system/OCA%5cUserExternal%5cIMAP:usercard.vcf?photo&size=32

Steps to reproduce

1. Log in to the web interface.
2. Click on the contact search button and search for a user with a profile picture.
3. The user avatar does not appear.
   

Expected behavior

The user's avatar image should be displayed.
(Security is set correctly to allow it. The image displays correctly in the contacts app.)

Installation method

Community Manual installation with Archive

Nextcloud Server version

27

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.2

Web server

None

Database engine version

MariaDB

Is this bug present after an update or on a fresh install?

Upgraded to a MAJOR version (ex. 22 to 23)

Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

{
    "system": {
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "tend.agardenwalk.net"
        ],
        "overwrite.cli.url": "https:\/\/tend.agardenwalk.net",
        "htaccess.RewriteBase": "\/",
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "objectstore": {
            "class": "\\OC\\Files\\ObjectStore\\S3",
            "arguments": {
                "bucket": "tend.agardenwalk.net",
                "autocreate": true,
                "key": "***REMOVED SENSITIVE VALUE***",
                "secret": "***REMOVED SENSITIVE VALUE***",
                "hostname": "s3.us-east-1.wasabisys.com",
                "region": "us-east-1",
                "port": 443,
                "use_ssl": true,
                "use_path_style": true
            }
        },
        "quota_include_external_storage": false,
        "share_folder": "\/Shared with Me",
        "dbtype": "mysql",
        "version": "27.1.4.1",
        "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",
        "memcache.distributed": "\\OC\\Memcache\\Redis",
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "filesystem_check_changes": 0,
        "filelocking.enabled": "true",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "port": 0,
            "dbindex": 0,
            "password": "***REMOVED SENSITIVE VALUE***",
            "timeout": 1.5
        },
        "enable_previews": true,
        "enabledPreviewProviders": [
            "OC\\Preview\\TXT",
            "OC\\Preview\\MarkDown",
            "OC\\Preview\\OpenDocument",
            "OC\\Preview\\PDF",
            "OC\\Preview\\MSOffice2003",
            "OC\\Preview\\MSOfficeDoc",
            "OC\\Preview\\Image",
            "OC\\Preview\\Photoshop",
            "OC\\Preview\\TIFF",
            "OC\\Preview\\SVG",
            "OC\\Preview\\Font",
            "OC\\Preview\\MP3",
            "OC\\Preview\\Movie",
            "OC\\Preview\\MKV",
            "OC\\Preview\\MP4",
            "OC\\Preview\\AVI"
        ],
        "remember_login_cookie_lifetime": 1296000,
        "session_lifetime": 86400,
        "session_relaxed_expiry": false,
        "session_keepalive": true,
        "auto_logout": false,
        "default_language": "en_US",
        "default_locale": "en_US",
        "default_phone_region": "en_US",
        "mail_smtpmode": "smtp",
        "mail_sendmailmode": "smtp",
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpauthtype": "LOGIN",
        "mail_smtpauth": 1,
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpport": "587",
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***",
        "maintenance": false,
        "simpleSignUpLink.shown": false,
        "user_backends": [
            {
                "class": "\\OCA\\UserExternal\\IMAP",
                "arguments": [
                    "email.agardenwalk.net",
                    993,
                    "ssl",
                    "agardenwalk.net",
                    true,
                    true
                ]
            }
        ],
        "theme": "",
        "loglevel": 2,
        "knowledgebaseenabled": false
    }
}

List of activated Apps

Enabled:
  - activity: 2.19.0
  - analytics: 4.11.1
  - announcementcenter: 6.7.0
  - bookmarks: 13.1.1
  - bruteforcesettings: 2.7.0
  - calendar: 4.6.0
  - calendar_resource_management: 0.5.0
  - circles: 27.0.1
  - cloud_federation_api: 1.10.0
  - comments: 1.17.0
  - contacts: 5.4.2
  - contactsinteraction: 1.8.0
  - cookbook: 0.10.3
  - dashboard: 7.7.0
  - dav: 1.27.0
  - deck: 1.11.2
  - drawio: 2.1.4
  - epubviewer: 1.5.3
  - external: 5.2.1
  - federatedfilesharing: 1.17.0
  - federation: 1.17.0
  - files: 1.22.0
  - files_3dmodelviewer: 0.0.12
  - files_accesscontrol: 1.17.1
  - files_antivirus: 5.4.0
  - files_archive: 1.1.3
  - files_external: 1.19.0
  - files_markdown: 2.4.1
  - files_mindmap: 0.0.30
  - files_pdfviewer: 2.8.0
  - files_reminders: 1.0.0
  - files_rightclick: 1.6.0
  - files_sharing: 1.19.0
  - files_texteditor: 2.15.1
  - files_trashbin: 1.17.0
  - files_versions: 1.20.0
  - files_zip: 1.4.0
  - firstrunwizard: 2.16.0
  - groupfolders: 15.3.1
  - integration_peertube: 1.0.2
  - logreader: 2.12.0
  - lookup_server_connector: 1.15.0
  - mail: 3.4.5
  - maps: 1.1.1
  - music: 1.9.1
  - news: 24.0.0
  - nextcloud_announcements: 1.16.0
  - notes: 4.8.1
  - notifications: 2.15.0
  - oauth2: 1.15.1
  - oidc: 0.7.1
  - password_policy: 1.17.0
  - passwords: 2023.11.30
  - photos: 2.3.0
  - previewgenerator: 5.4.0
  - privacy: 1.11.0
  - provisioning_api: 1.17.0
  - quota_warning: 1.18.0
  - recommendations: 1.6.0
  - related_resources: 1.2.0
  - richdocuments: 8.2.3
  - serverinfo: 1.17.0
  - settings: 1.9.0
  - sharebymail: 1.17.0
  - side_menu: 3.11.2
  - sketch_picker: 1.0.1
  - spreed: 17.1.3
  - support: 1.10.0
  - survey_client: 1.15.0
  - systemtags: 1.17.0
  - tasks: 0.15.0
  - text: 3.8.0
  - theming: 2.2.0
  - theming_customcss: 1.15.0
  - twofactor_backupcodes: 1.16.0
  - updatenotification: 1.17.0
  - user_external: 3.2.0
  - user_status: 1.7.0
  - viewer: 2.1.0
  - weather_status: 1.7.0
  - welcome: 1.0.10
  - workflowengine: 2.9.0
Disabled:
  - admin_audit: 1.17.0
  - encryption: 2.15.0
  - suspicious_login: 5.0.0
  - twofactor_totp: 9.0.0
  - user_ldap: 1.17.0

Nextcloud Signing status

No errors have been found.

Nextcloud Logs

empty

Additional info

The issue is the same in Brave, Chrome, and Firefox
Escaping the '\' in the inspector/debugger displays the image correctly.

Start with the contact search avatar flow and the generated DAV system address-book URL for UserExternal_IMAP; no source file or test is named in the report. Reproduce the missing avatar, then verify that the URL handles the backslashes and the image displays, adding a regression test if the relevant test area is found.