linux – how to restrict access to subfolders on samba?

I need that some users from the domain group ‘Security Unit’ (samba the list of users takes from Active Directory) did not have access to the so-called Secret directory.
How can this be implemented?

(test)
    comment = test folder
    path = /folder2/test
    browseable = yes
    read only = no
    inherit permissions = yes
    create mask = 0770
    directory mask = 0770
    valid users = "@kumar.inSecurity Unit"
    admin users = "@kumar.inSpecial Domain Administrators"
    vfs objects = full_audit
    full_audit:prefix = %u|%I|%S
    full_audit:failure = none
    full_audit:success = mkdir rmdir open read write pwrite sendfile rename unlink lock
    full_audit:facility = local5
    full_audit:priority = notice

the test directory has the following structure

test
├── public
└── secret