On your Mac, you have Apache with php installed. You can contact the default site on you computer at http://localhost
On Mac OSX the document root is at /Library/WebServer/Documents.
In preferences under 'Sharing' you will have to have the 'web sharing' option
checked to contact it with your browser.
Login processing is a sensitive issue. I have developed a login/register system
in php which reasonably secure. It would probably not serve for sensitive data
like payment/credit card processing.
Interested: reply with contact info other than site link.