Oracle Database
NOTE: I no longer have access to an Oracle database, however, from what I can tell it all works the same with CakePHP 5 as it did with CakePHP 4.
CakePHP 5 does not provide core support for Oracle databases. An Oracle database driver plugin is available from CakeDC here: https://github.com/CakeDC/cakephp-oracle-driver
It's almost as easy as following the directions there, but there are a few "gotchas" with Oracle.