MySQL Governor allows upgrades to unsupported versions of MariaDB

Symptoms

MariaDB 10.4 cause issues with loading phpMyAdmin from the cPanel interface. You will also see errors changing MySQL user passwords and assigning them to databases. An example error is below:

Cpanel::Exception::Database::Error/(XID owejf4j) The system received an error from the
 “MySQL” database “mysql”: ER_PASSWORD_NO_MATCH (Can't find any matching row in the user table) 

Description 

MariaDB 10.4 introduces a number change in the authentication process method:

Authentication from MariaDB 10.4

If you are on CloudLinux and use the MySQL Governor system to manage your MySQL/MariaDB installation, the upgrade path allows you to upgrade to MariaDB 10.4 or 10.5.  These versions of MariaDB are not yet supported by the cPanel & WHM software.  Currently, the highest version of MariaDB we support is 10.3.   

MySQL Governor should not permit you to upgrade past 10.3 until 10.4 is supported.  The CloudLinux team has a case open to add appropriate warnings to MySQL Governor should attempts be made to upgrade to 10.4 or 10.5.

Workaround

If it's too late and you have already upgraded past 10.3, there is no downgrade path.  Neither cPanel, CloudLinux nor even the MariaDB developers support a downgrade.  You will need to make backups of all databases, completely remove MariaDB 10.4 and install MariaDB 10.3 and then restore your databases.  You may even need to rely on previous backups that you took before the upgrade to 10.4.