PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Implementing User Authentication
587
Listing 27.12
Continued
if (!$result) {
throw new Exception('Could not log you in.');
}
if ($result->num_rows>0) {
return true;
} else {
throw new Exception('Could not log you in.');
}
}
As you can see, the login() function connects to the database and checks that there is a
user with the username and password combination supplied. It returns true if there is or
throws an exception if there is not or if the user’s credentials could not be checked.
The check_valid_user() function does not connect to the database again, but
instead just checks that the user has a registered session—that is, that he has already
logged in.This function is shown in Listing 27.13.
Listing 27.13 check_valid_user()Function from user_auth_fns.php—This
Function Checks That the User Has a Valid Session
function check_valid_user() {
// see if somebody is logged in and notify them if not
if (isset($_SESSION['valid_user'])) {
echo "Logged in as ".$_SESSION['valid_user'].".";
} else {
// they are not logged in
do_html_heading('Problem:');
echo 'You are not logged in.';
do_html_url('login.php', 'Login');
do_html_footer();
exit;
}
}
If the user is not logged in, the function will tell him he has to be logged in to see this
page, and give him a link to the login page.
Logging Out
You might have noticed the link marked Logout on the menu in Figure 27.6.This is a
link to the logout.php script; the code for this script is shown in Listing 27.14.