Hey anyway I didn't found anything usefull...
Just that apparently we are not doing right, they all seems to use security = user indeed of security = ads. But that's not clear for me.
I cannot help you further.
Maybe you can. Try to get as much as info as you can.
Here is a "security = user" smb.conf file:
Then a post where someone is trying to do exactly the same as you are trying to. And he works it but I don't know how; very interesting:
And finally, this is not usefull at all, but maybe you doesn't know it and it will guide you:
Have fun & Good Luck