The Password Hasher component was added in [#39802](https://github.com/symfony/symfony/pull/39802), there's [this blog post announcement](https://symfony.com/blog/new-in-symfony-5-3-passwordhasher-component), but there's no documentation yet. The Password Hasher [README.md](https://github.com/symfony/password-hasher/blob/5.3/README.md) has a [Documentation link](https://symfony.com/doc/current/password-hasher.html) (which currently links to a 404).