Hooks and filters for log-in to allow added CAPTCHA

[CyberDexter]

I'd like to suggest the adding of captcha anti-bot to the login page.

[msmalley]

That would need to be done via hooks and filters, rather than being part of core...

Most bots would not be able to log-in as everything is created and served client-side.

Nonetheless, we do need more hooks and filters in place, so this seems like a good excuse to add more!