I'm new here so feel free to hate in case I didn't follow "something"
Secondly - I doubt I can report this as bug or issue as nowhere found it could be supported, so this is more like "is it possible" and "request for help"
However up to 9.0.2 solution worked fine and this was:
Steps to reproduce
1. Make on a server filesystem directory [/my_data_dir] not owned by www-data (or other user used for apache/nginx) and fill up with data/files
2. Make this directory readable and "executable", as well as files inside, for www-data user [chmod -R 755 /my_data_dir]
3. Make a symlink to this directory in owncloud user home [ ln -s /my_data_dir data/VIPuser/files/my_data]
4. Try to scan it by occ and/or enter from web. You will be given message that this operation is not allowed and in log you will find that remote.php issues 403 on webdav.
To see contents of my_dir
Operating system: Ubuntu 16 LTS
Web server: Apache
ownCloud version (see ownCloud admin page): 188.8.131.52
Updated from an older ownCloud or fresh install: 9.0.2
So, I've been using this way from version 8 and never had issue. It worked perfectly. Yesterday did upgrade to 184.108.40.206
(and applied changes for bugs
And it stopped working this way.
All "normal" functionality works but this one stopped.
So now the question is is it possible by configuration to make owncloud to act same as before. This is very important part of functionality as I will not put all of the data from /my_data_dir under owncloud. This directory is also accessible by other channels and "very very unlikely" I would want to change it to be fully owned by www-data as well.
Any hints welcome...