unknow variable validate_password

[Long Nguyen]

I run mysql 5.7.27 on Ubuntu 18.04. I have installed validate_password plugin and have it loaded in the config file with

plugin-load=server_audit=server_audit.so

No issue there.

However when I put in a password validation related parameters like
"validate_password=FORCE_PLUS_PERMANENT" or "validate_password_length = 10",
mysql failed to start up. It gave an 'unknown variable" message.

The variables were put under the [mysqld] section.

Just wonder if anyone experienced the same issue.

Thanks