In order to have these functions available, you must compile PHP with support for the mysqli extension.
When running a PHP version before 7.1.16, or PHP 7.2 before 7.2.4, set MySQL 8 Server's default password plugin to mysql_native_password or else you will see errors similar to The server requested authentication method unknown to the client [caching_sha2_password] even when caching_sha2_password is not used.
This is because MySQL 8 defaults to caching_sha2_password, a
plugin that is not recognized by the older PHP (mysqlnd)
releases. Instead, change it by setting
caching_sha2_password plugin will be
supported in a future PHP release. In the meantime, the
extension does support it.