MySQL Error: Authentication plugin 'caching_sha2_password' cannot be loaded I just installed MySQL Ver 14.14 Distrib 5.7.22 with Homebrew on my macOS v10.13.4.
I ran the command:
brew install mysql 

After the installation completed, as directed by Homebrew, I ran the command:
mysql_secure_installation
and was returned the error: Error: Authentication plugin 'caching_sha2_password' cannot be loaded: dlopen(/usr/local/Cellar/mysql/5.7.22/lib/plugin/caching_sha2_password.so, 2): image not found   

I tried a few things like changing default_authentication_plugin to mysql_native_password in the my.cnf file but it still throws the same error. 

Next I tried running:
mysql_upgrade -u root
and I was thrown the same error again mysql_upgrade: Got error: 2059: Authentication plugin 'caching_sha2_password' cannot be loaded: dlopen(/usr/local/Cellar/mysql/5.7.22/lib/plugin/caching_sha2_password.so, 2): image not found while connecting to the MySQL server
Upgrade process encountered error and will not continue.

Any help is appreciated.
So, I found the running process of mysqld by sudo lsof -i tcp:3306 then I killed it using sudo kill -9 &lt;PID&gt;.
After this I tried $ mysql_secure_installation again but ran into a new error Error: Can't connect to local MySQL server through socket '/tmp/mysql.sock' (61)
After trying a few fixes for getting mysql.sock to work, I started the MySQL server with
$ sudo mysql.server start
then went ahead with $ mysql_secure_installation to set password for the root user. 

This worked for me finally.

Note: Homebrew asks you to first do mysql_secure_installation before starting the MySQL server for the first time but that just made me run into endless loop of errors.