Android CalDAV-Sync does not sync after Nextcloud upgraded to 18.0.4

Steps to reproduce

Add a calender item using the Nextcloud Calendar App
Add another item in the Android calendar
Await periodic sync or force a manual sync

Expected behaviour

Item no. 1 should appear in the Android calendar Item no. 2 should appear in the Nextcloud calendar

Actual behaviour

Absolutely nothing happens (CardDAV is not affected and works as expected)

Analysis

A client access without credentials yields a 404 error from the server. On Nextcloud 18.0.3 (and before) it yields a 401 error and retries (successfully) with credentials. I tracked it down to commit ce8f194a2a77a5f5cad62d9de4da033a67b4c927 - reverting this commit restored the previous behaviour and solved the problem.

Server configuration

Operating system: Ubuntu 18.04.4 LTS

Web server: Apache 2.4.29

Database: MariaDB 10.1.44

PHP version: PHP 7.2.24

Nextcloud version: (see Nextcloud admin page) 18.0.4

Updated from an older Nextcloud/ownCloud or fresh install: Updated from 18.0.3

Where did you install Nextcloud from:

Signing status:

Signing status

``` No errors have been found. ```

List of activated apps:

App list

``` Enabled: - accessibility: 1.4.0 - activity: 2.11.0 - apporder: 0.10.0 - calendar: 2.0.3 - cloud_federation_api: 1.1.0 - contacts: 3.3.0 - dav: 1.14.0 - deck: 1.0.1 - encryption: 2.6.0 - federatedfilesharing: 1.8.0 - files: 1.13.1 - files_antivirus: 2.4.1 - files_ebookreader: 0.0.1 - files_pdfviewer: 1.7.0 - files_readmemd: 1.1.4 - files_rightclick: 0.15.2 - files_sharing: 1.10.1 - files_trashbin: 1.8.0 - files_videoplayer: 1.7.0 - firstrunwizard: 2.7.0 - gpxpod: 4.2.1 - logreader: 2.3.0 - lookup_server_connector: 1.6.0 - music: 0.14.1 - nextcloud_announcements: 1.7.0 - notes: 3.4.0 - notifications: 2.6.0 - oauth2: 1.6.0 - password_policy: 1.8.0 - phonetrack: 0.6.3 - photos: 1.0.0 - polls: 1.4.3 - privacy: 1.2.0 - provisioning_api: 1.8.0 - qownnotesapi: 20.1.0 - serverinfo: 1.8.0 - settings: 1.0.0 - sharebymail: 1.8.0 - support: 1.1.0 - survey_client: 1.6.0 - tasks: 0.13.1 - text: 2.0.0 - theming: 1.9.0 - twofactor_backupcodes: 1.7.0 - twofactor_totp: 4.1.3 - updatenotification: 1.8.0 - viewer: 1.2.0 - workflowengine: 2.0.0 Disabled: - admin_audit - comments - federation - files_external - files_versions - recommendations - systemtags - user_ldap ```

Nextcloud configuration:

Config report

``` { "system": { "instanceid": "***REMOVED SENSITIVE VALUE***", "passwordsalt": "***REMOVED SENSITIVE VALUE***", "hashingCost": 10, "trusted_domains": [ "mads.alarsen.net" ], "datadirectory": "***REMOVED SENSITIVE VALUE***", "version": "18.0.4.2", "dbtype": "mysql", "dbhost": "***REMOVED SENSITIVE VALUE***", "dbname": "***REMOVED SENSITIVE VALUE***", "dbuser": "***REMOVED SENSITIVE VALUE***", "dbpassword": "***REMOVED SENSITIVE VALUE***", "dbtableprefix": "oc_", "installed": true, "defaultapp": "apporder", "knowledgebaseenabled": true, "enable_avatars": true, "default_language": "de", "allow_user_to_change_display_name": false, "remember_login_cookie_lifetime": 1296000, "session_lifetime": 86400, "session_keepalive": true, "memcache.local": "\\OC\\Memcache\\Redis", "memcache.locking": "\\OC\\Memcache\\Redis", "filelocking.enabled": "true", "redis": { "host": "***REMOVED SENSITIVE VALUE***", "port": 0, "timeout": 0 }, "asset-pipeline.enabled": false, "mail_domain": "***REMOVED SENSITIVE VALUE***", "mail_from_address": "***REMOVED SENSITIVE VALUE***", "mail_smtpdebug": false, "mail_smtpmode": "smtp", "mail_smtphost": "***REMOVED SENSITIVE VALUE***", "mail_smtpport": "587", "trashbin_retention_obligation": "auto, 30", "logtimezone": "Europe\/Berlin", "log_rotate_size": 10485760, "skeletondirectory": "\/var\/www\/nextcloud\/local\/skeleton", "overwrite.cli.url": "https:\/\/mads.alarsen.net\/owncloud", "htaccess.RewriteBase": "\/owncloud", "updatechecker": true, "updater.release.channel": "stable", "appstoreenabled": true, "apps_paths": [ { "path": "\/var\/www\/nextcloud\/apps", "url": "\/apps", "writable": true } ], "enable_previews": true, "forcessl": true, "theme": "", "secret": "***REMOVED SENSITIVE VALUE***", "maintenance": false, "singleuser": false, "loglevel": 2, "mail_sendmailmode": "smtp", "app_install_overwrite": [ "calendar", "files_ebookreader", "files_readmemd" ], "mysql.utf8mb4": true } } ```

Are you using external storage, if yes which one: local/smb/sftp/... No

Are you using encryption: yes/no Yes

Are you using an external user-backend, if yes which one: LDAP/ActiveDirectory/Webdav/... No

Client configuration

Browser: CalDAV Sync (latest version)

Operating system: Android 8.0

Logs

Web server error log

Web server error log with error occurring (18.0.4)

``` "OPTIONS /owncloud/remote.php/dav/calendars/// HTTP/1.1" 404 238 ```

Web server error log without error (18.0.3)

``` "OPTIONS /owncloud/remote.php/dav/calendars/// HTTP/1.1" 401 450 "OPTIONS /owncloud/remote.php/dav/calendars/// HTTP/1.1" 200 - ```

Nextcloud log (data/nextcloud.log)

Nextcloud log

``` Nothing reported. ```

Browser log

``` CalDAV Sync fails silently :-( ```

nextcloud / server