How would you set up a login page for BootstrapStudio? And do they have anything already built in?
W3Schools gives some general guidance here https://www.w3schools.com/howto/howto_css_login_form.asp but I suspect what you might be really asking is: "Does BSS have any "backend" functionality built in?" (see the direction in the above page to W3S tutorial page on PHP) and to which the answer is "Not so far as I know?" -- and this is an aspect of BSS I'm not that familiar with either, but check out what you can find here:
https://bootstrapstudio.io/forums/search/php+login/
front-end builders all (BSS, CC, MBR) all tend to rely on third-party add-ins for this, but hopefully you'll strike it lucky and a proprietor of one for BSS will log in for you. I'm interested in this myself.