If it’s on the same nethserver AD you might do it by creating an AD user and using it for the system service (syncthing@theuser.service). Syncthing will access the local filesystem.
If file permissions are important to you, do the tests on a separate share. If you need to, you can reset the shared folder permissions, and also have the option of setting the UMask parameter in the systemd service file.
Not the same case but, if it’s of help, @JOduMonT kindly shared these notes on syncthing: