Well I got it working 😆 now.
Problem 1: I was lying.
Taking a closer look at the filesystem, permissions of …/public were wrong (I chowned it to 755 instead of chmodding it 😳 )
Totally my mistake. I apologize for wasting people´s time.
Also my mistake, but worth a note: whitespaces after a value will not be stripped when key/value-pairs are loaded from the .conf, therefore “password” and “password ” are not the same. This is easy to miss, if you do not expect this behaviour…
Thanks for replying