Support for frontend *sha_* password plugins

[svetasmirnova]

Here is an extension for the feature request at #2229

While ProxySQL supports sha_ password plugins on the backend side, it requires storing them as plain text in the mysql_users table. This is not acceptable for most setups. Therefore we need full - backend and frontend - support for sha_ plugins and they should be stored in the mysql_users table encripted.

This is especially important because starting from MySQL 8.0.34 mysql_native_password is marked as deprecated. It still exists in MySQL 8.2 but could be easily removed in 8.3 or 8.4.

[asivado]

Work on this feature is already underway and it will be included in a future release.

Concerning the potential removal of mysql_native_password authentication: even if it does happen, users will still be able to use ProxySQL for backend authentication in the meantime, since it does already support sha256_password and caching_sha2_password for backend authentication.

[svetasmirnova]

@asivado thank you for the feedback. I am looking forward for this feature!

Regarding current backend implementation: I am sorry, but this does not work for most users because ProxySQL requires storing passwords in table mysql_users as plain text, not encrypted. This is even less secure than using the old mysql_native_password plugin.

[renecannao]

Support added in PR #4258 , already merged

[bethford-psyonix]

Thank you