Create user with require ssl throws syntax error

On execution of this simple user creation statement

CREATE USER 'repl'@'%.mydomain.com' IDENTIFIED BY 'blablabla' REQUIRE SSL;

this error message is returned:

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'REQUIRE SSL' at line 1

The same error message appears if the user is first created without the require constraint but then altered later like

ALTER USER 'repl'@'%.mydomain.com' REQUIRE SSL;

Thanks for any advice in advance.