How to change the login plugin from mysql_native_password to caching_sha2_password

[Liang Cheng]

Hi,
Most of our environments are mysql5.7 and we are trying MySQL8 recently. One difference between 5.7.x and 8.0 is that the default login plugin is changed from mysql_native_password to caching_sha2_password.
For now, we know that we can upgrade the existing 5.7 environments to 8.0 by specifying the plugin to mysql_native_password. But mysql_native_password will be deprecated anyway. So we wonder that how to change login plugin of existing users from mysql_native_password to caching_sha2_password in case that we want to plan upgrade 5.7 to latest 8.0+. We know how to change the login plugin for any user manually created by us.
But we don't know how to migrate for system users, e.g. mysql.sys, mysql.session and the internal users created by mysqlrouter, I suspect the login plugin of mysqlrouter user maybe related to plugin type of system user.

| mysql_router1_9dpfyggnr7bg | % | mysql_native_password |
| mysql_router1_r2dvd2ouvpsh | % | mysql_native_password |
| mysql_router8_nnuisdqf5bgi | % | mysql_native_password |
| mysql_router8_q67c850fzp1p | % | mysql_native_password |
| replication_user | % | caching_sha2_password |
| root | % | caching_sha2_password |
| mysql.infoschema | localhost | caching_sha2_password |
| mysql.session | localhost | mysql_native_password |
| mysql.sys | localhost | mysql_native_password |

Please share some knowledge, thanks a lot.