docker+nginx and xdebug

Hi.
I am running a docker container with nginx, php5 and php5-xdebug.
The container is run via

docker run -p 8001:80 -p 8443:443 -p 9001:9001 \
 -v $DIR/src:/home/myuser/src:ro \
 -v $DIR/www:/home/myuser/www:ro \
...

So I can access {projectroot}/www/test.php via https://localhost:8443/local/test.php

PHP Storm is also listening for PHP Debug connections (I clicked the button). With the built-in webserver I was able to successfully break on breakpoints.
However I can't seem to get xdebug (i.e. using breakpoints etc.) running using my docker setup.

phpinfo says:
PHP Version 5.6.40-0+deb8u12

Additional ini-files parsend: .../etc/php5/fpm/conf.d/20-xdebug.ini...
Contents of that file: zend_extension=xdebug.so

I also tried Validate Debugger Configuration on Web Server:
[x] Local Web Server or Shared Folder
Path to create validation script: /home/foo/bar/www/
Url to validation script: https://localhost:8443/local/
Specified URL is not reachable, caused by: 'No name matching localhost found'

I can access https://localhost:8443/local/ with no problem in the browser (also have the xdebug extensions installed).
If I create a file /home/foo/bar/www/test.php, then I can access it via https://localhost:8443/local/test.php

In Settings > Tools > Server Certificates I have added the server certificates and also "Accept non-trusted certificates automatically" is checked.

Not sure what to do next, also bugs me, that I can't get "Web Server Debug Validation" to work.

Thanks for your time.