Use PHP to detect which htaccess user signed in?

I'm constructing an upload so people I know can send me files securely, and with ease. But I want to design it just so, that when one of my friends sign in with their sign-in (it's going to an .htaccess login), I can establish that in PHP and log their file into a database associated with their account.

In short, I need PHP to be able to detect who is signed in so I can pass that data to a database.

Is there any possible way of doing that?