X Plugin supports MySQL user accounts created with the caching_sha2_password authentication plugin. For more information on this plugin, see Section 8.4.1.2, “Caching SHA-2 Pluggable Authentication”. You can use X Plugin to authenticate against such accounts using non-SSL connections with SHA256_MEMORY authentication and SSL connections with PLAIN authentication.

Although the caching_sha2_password authentication plugin holds an authentication cache, this cache is not shared with X Plugin, so X Plugin uses its own authentication cache for SHA256_MEMORY authentication. The X Plugin authentication cache stores hashes of user account passwords, and cannot be accessed using SQL. If a user account is modified or removed, the relevant entries are removed from the cache. The X Plugin authentication cache is maintained by the mysqlx_cache_cleaner plugin, which is enabled by default, and has no related system variables or status variables.

Before you can use non-SSL X Protocol connections to authenticate an account that uses the caching_sha2_password authentication plugin, the account must have authenticated at least once over an X Protocol connection with SSL, to supply the password to the X Plugin authentication cache. Once this initial authentication over SSL has succeeded, non-SSL X Protocol connections can be used.

It is possible to disable the mysqlx_cache_cleaner plugin by starting the MySQL server with the option --mysqlx_cache_cleaner=0. If you do this, the X Plugin authentication cache is disabled, and therefore SSL must always be used for X Protocol connections when authenticating with SHA256_MEMORY authentication.