Using Session Variables for Login Security
Since session variables exist for the duration of a session we can require
a user to login through a page and set a session variable if they do so
appropriately. All other pages in the site can have a code snippet
at the very beginning that will redirect the user back to the login page
if they haven't completed it correctly and try to bypass it.
To illustrate this we will need three pages.
The first page should be called site_login.php.
<title>Login Page for the Site</title>
<body bgcolor="003044" text="cccccc">
<form action="site_login_processing.php" method = "post">
<td align=center colspan=2><h3Please enter the password</h3></td>
<td align=right><b>Password: </b></td>
<td><input type="password" name="txt_password", size=10></td>
<td align=center colspan=2><input type="submit" name="cmd_submit" value = "Submit Password"></td>
|Now we need the processing page. The user is not likely to even see this page. You should call it site_login_processing.php.|
// obtaining the information from the form and
// using it to determine redirection
if ($txt_password != "letmein")
|Notice how the if - else structure depends on the
user's input and does certain things based on its value.
The last page in our trio is a very pared down index page that does little more than test for the presence of the session variable $_SESSION["valid_user"]. You should call this page site_index.php.
// checking to see whether the user has
// entered a valid password
if ($_SESSION["valid_user"] != "valid")
|This sort of PHP code segment needs to be placed at the beginning of every other page within the web to ensure the user has the valid password.|