Localhost errors with MariaDB server

What causes this error when using mysql connection ? :-
“Host ‘localhost’ is not allowed to connect to this MariaDB server”

Maybe this can help:

This error is happening when trying to use ExeOutputs adminer, The error:-
Host ‘localhost’ is not allowed to connect to this MariaDB server.

Be sure to add the connection port to localhost, such as localhost:3306 (check which port was used in ExeOutput by clicking on the corresponding link).