Implementing opaque isn't overly hard. You can find pseudocode, implementations, state machine diagrams, etc, online. Here's a good post that links to implemented code:
https://blog.cloudflare.com/opaque-oblivious-passwords/I know nothing of framework support, I don't use frameworks. I'm likely going to contribute some open source code in the near future from my company to simplify things though.
But you could also just have your client do:
salt = sha256("your company name goes here" + username)
password_hash = pbkdf2(plaintext_password, salt)
and get some nice benefits.
> How would I ensure that my code for PAKE could not be overwritten if a hacker took over part of my server?
Depends on the server and the level of control. But it'll help in a number of cases. You're assuming the attacker has full control over the web-page's contents (among other things - even if an attacker had the web page's contents CORS means they couldn't send http only cookies to an attacker controlled server), which is a very specific, powerful position to be in.