Regarding https://docs.oracle.com/cd/E52668_01/E54669/html/ol7-s4-fsadmin.html
According to my tests, using credentials file and CIFS only works when /sbin/mount.cifs exists. Otherwise, you'll see a message like: "CIFS VFS: No username specified". It simply requires the installation of the cifs-utils package.
Perhaps the documentation should include an example how to create a credentials file and a note to install cifs-utils.