I do have the same issue. Created an account and added the user account and the user group to the webdav drive in file system via ACL.
With "No Authentication" chosen in webdav configuration, I can map the drive via Windows system and works perfectly fine. However, use browser, I don't need to login and just will let me enter the site without login and with only "read" (and "execute" I guess) but not "write". And same to map with Ubuntu, no matter I tried to use any account set in ACL, <user>@<ip>:port, to force to enter with the user account, still not prompt require password fill in but just let me in, and same with web login, I cannot enter with the correct user with right privileges.
When changed to "basic authentication" requirements, I found that it could only be set to "webdav" account but this "webdav" account is only a default http login account but not related to the "webdav" account in file system and related to any of its privileges. Other accounts login will not work.
I may need some help on how to make it works. I don't need to prompt web page login in web browser but could just login with correct user login to the file system to use the file.