Hi there!
Are you referring to the standardised basic HTTP Authentication Scheme as per the RFC 7617 specs?
In my experience this kind of basic authentication was rather popular back in the days before programming languages like PHP and Ruby become so popular that patterns of more sophisticated ways of dealing with authentication emerged. And when frameworks based on these programming languages made this even easier, I think this way of authenticating user has become a really rare sight these days.
Getting up and running with a developer friendly, battle tested and secure authentication scheme is done in minutes with Laravel as an example. Doing something similar with HTTP Authentication would be possible to some extent, but I am personally not aware of any ready made solutions for it. But there might be someone who has made a package of some sorts that you could study the source code for as an inspiration or just to learn how you could utilise PHP for such a task.
I could think of a possible scenario where I would have a web app in production or at least accessible by anyone on in the internet, but where I wanted to only let some specific people access the website regardless of the authentication scheme provided by the framework (or even if it were custom made).
I hope I understood your question correctly, and if not I apologise.