Problem

Start from MySQL 8, the authentication plugin is changed to "caching_sha2_password".

Therefore, phpMyAdmin or other client tools will get "Public Key Retrieval is not allowed"problem.

Solution

We changed the authentication plugin to "mysql_native_password".

If you use docker. You need do this first.
$sudo docker exec -it docker_run_name bash
Example: $ sudo docker exec -it mysql bash

$ mysql -u root -p

mysql> use mysql

mysql> select host, user from user;
+-----------+------------------+
| host      | user             |
+-----------+------------------+
| %         | root             |
| localhost | mysql.infoschema |
| localhost | mysql.session    |
| localhost | mysql.sys        |
| localhost | root             |
+-----------+------------------+
5 rows in set (0.00 sec)

mysql> ALTER USER 'root'@'%' IDENTIFIED WITH mysql_native_password BY 'Your New Password';
Query OK, 0 rows affected (0.08 sec)

mysql> FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.01 sec)

Test