Comments - Upgrade from old Mysql install to recent Mariadb.

When you say starts to fail at the user database, this is probably because the MySQL 5.7 users are using SHA-256 - you can check which MySQL users are using SHA-256 by executing:

SELECT user, plugin FROM mysql.user where plugin like "%sha%";

You can change the user/s to use a protocol compatible with both MySQL and MariaDB with:

ALTER USER user_name IDENTIFIED WITH mysql_native_password BY  'new_password';

This can all be done on the database side, and there should be no need to change anything on the application side.

This doesn't help: I still have to go into the application, find where it stores the password and then change it to the new password, or copy the old password into the commandline you're giving. :-(

OK. Maybe it helps a little bit. I could find a first application, extract the password, change the password to the new format for testing, and then I'd know that on D-day I can dump the database, and import it into mariadb.

Testing: So your first commandline gave

  mysql> SELECT user, plugin FROM mysql.user where plugin like "%sha%";
  Empty set (0.00 sec)

and then I tried:

 mysql> SELECT user, plugin FROM mysql.user ;
 +------------------+-----------------------+
 | user             | plugin                | 
 +------------------+-----------------------+
 | root             | mysql_native_password |
 | root             | mysql_native_password |
 | xxxx....         | mysql_native_password |
...

So. All users are already on mysql_native_password.