<?php
    $function = $_GET['function'];

    if($function == "login"){
        $userName = $_GET['username'];
        $saltedPass = $_GET['pass'];
        //login query
        //return true or false
    }
?>

$check = HTTPrequest('www.domain.com/functions.php?function=login&username=mike&pass=343iubgfdg34tJHVvr23').read();
if($check == true){
    //login
}
else{
    //wrong username or pass
}