Had an issue today on a freshly installed MariaDB server.

Was unable to login from adminer and PhpMyAdmin, even though through the console it was working without issued.

The answers lies in the "plugin" column on the user table of mysql database. You have to remove the "unix_socket" in it and Flush Privileges to appl. And that's it ! Enjoy and thanks to https://superuser.com/questions/603026/mysql-how-to-fix-access-denied-for-user-rootlocalhost for the hint.

MariaDB [(none)]> UPDATE mysql.user SET plugin = "" WHERE User = 'root';
Query OK, 1 row affected (0.00 sec)
Rows matched: 2  Changed: 1  Warnings: 0

Query OK, 0 rows affected (0.00 sec)