Steps to reproduce

1. Get Nextcloud 11.0.1
2. ./occ maintenance:install --data-dir=/var/www/html/data --database mysql --database-name nextcloud --database-user nextcloud --database-pass nextcloud --admin-user admin --admin-pass admin
3. Ensure the setup works at http://localhost/ as expected
4. Put a reverse proxy called tux.example.net in front of it – including HTTPS
5. Ensure that Nextcloud is installed on /, but access using reverse proxy happens via /my-nextcloud
6. Visit https://tux.example.net/my-nextcloud/settings/admin
7. Press "Start update" button
8. Receive "Check for expected files: Parsing response failed. […]"
9. Figure out that the POST request went to https://tux.example.net/updater/index.php rather https://tux.example.net/my-nextcloud/updater/index.php

Expected behaviour

Webbased Nextcloud updater fails in reverse proxy scenario with / vs. /something

Actual behaviour

Properly working webbased Nextcloud updater even in reverse proxy scenario with / vs. /something

Server configuration

Operating system: Red Hat Enterprise Linux 7.3, but doesn't matter here anyway.

Web server: Apache Webserver 2.4, but doesn't matter here anyway.

Database: MariaDB 5.5, but doesn't matter here anyway.

PHP version: 7.1 (via Remi Safe repository), but doesn't matter here anyway.

Nextcloud version: 11.0.1

Updated from an older Nextcloud/ownCloud or fresh install: Fresh installation.

Where did you install Nextcloud from: https://download.nextcloud.com/server/releases/nextcloud-11.0.1.tar.bz2

Signing status: N/A

List of activated apps: N/A

The content of config/config.php:

  'trusted_domains' => 
  array (
    0 => 'localhost',
    1 => 'tux.example.net',
  ),
  'overwrite.cli.url' => 'https://tux.example.net/my-nextcloud',
  'overwritehost' => 'tux.example.net',
  'overwriteprotocol' => 'https',
  'overwritewebroot' => '/my-nextcloud',
  'trusted_proxies' => 
  array (
    1 => '172.17.0.1',
  ),
  'overwritecondaddr' => '^172\\.17\\.0\\.1$',
  'htaccess.RewriteBase' => '/',

Are you using external storage, if yes which one: No external storage.

Are you using encryption: No

Are you using an external user-backend, if yes which one: No