Authentication rework - draft2 - DONOTMERGE

[renecannao]

Support for caching_sha2_password .
New variable mysql-default_authentication_plugin .
Deprecate variable admin-hash_passwords #4218 .

Although fully functional, it is still a work in progress.

It also deprecate PR #4136

[renecannao]

retest this please

[renecannao]

retest this please

[yakirgb]

@renecannao Is it will be global variable or per user ?
Because if doing migration of users from mysql_native_password to caching_sha2_password , we will do it user by user and not for all users together .

[renecannao]

@yakirgb : the new variable MUST be global , not just because it is the "default" plugin, but because in MySQL protocol authentication, the server (proxysql in this case) is the first that specifies the default authentication method, even before the client sends its username.
That said, depending from how passwords are stored in mysql_users.password , user can use either mysql_native_password or caching_sha2_password . And proxysql can use the same or a different authentication method when connecting to the backend.

[yakirgb]

Thank you for the explain.

[mirostauder]

Can one of the admins verify this patch?