I have made a login page to my website. If the user id and password matches in the database, the user is directed to page1.php but if the user knows the URL for the page1.php, he can bypass the login page. How do i solve this problem ? I know the problem is so trivial but I am new to the web development and unable to find a solution to this problem. The solution seems to be using the seesion token. But, i have no idea how to use it to deny access or directly load page1.php

```
<?php

/*** begin our session ***/
session_start();

/*** set a form token ***/
$form_token = md5( uniqid('auth', true) );

/*** set the session form token ***/
$_SESSION['form_token'] = $form_token;
?>

<!DOCTYPE html>
<!--[if lt IE 7]> <html class="lt-ie9 lt-ie8 lt-ie7" lang="en"> <![endif]-->
<!--[if IE 7]> <html class="lt-ie9 lt-ie8" lang="en"> <![endif]-->
<!--[if IE 8]> <html class="lt-ie9" lang="en"> <![endif]-->
<!--[if gt IE 8]><!--> <html lang="en"> <!--<![endif]-->
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
  <link rel="stylesheet" href="css/style.css">
  <!--[if lt IE 9]><script src="//html5shim.googlecode.com/svn/trunk/html5.js"></script><![endif]-->
</head>
<body>

  <form method="post" action="login.php" class="login">
    <p>
       <label for="username">Username:</label>
      <input type="text" name="username" id="username" style="width:300px" required placeholder="enter username" maxlength="20">
    </p>

    <p>
      <label for="password">Password:</label>
      <input type="password" name="password" id="password" style="width:300px" required placeholder="enter password" maxlength="20">
    </p>

    <p class="login-submit">
      <input type="hidden" name="form_token" value="<?php echo $form_token; ?>" />
      <button type="submit" class="login-button" value="&rarr; Login">Login</button>
    </p>

    <p class="forgot-password"><a href="index.html">Forgot your password?</a></p>
  </form>

  <sup style="color:#777; padding-left:550px;"> ** both username and password must be alpha-numeric between 4-20 characters</sup>

</body>
</html>

```

This is my php file that handles the login form input

```
<?php

/*** begin our session ***/
session_start();

/*** check if the users is already logged in ***/
if(isset( $_SESSION['user_id'] ))
{
    $message = 'Users is already logged in';
}
/*** check that both the username, password have been submitted ***/
if(!isset( $_POST['username'], $_POST['password']))
{
    $message = 'Please enter a valid username and password';
}
/*** check the username is the correct length ***/
elseif (strlen( $_POST['username']) > 20 || strlen($_POST['username']) < 4)
{
    $message = 'Incorrect Length for Username';
}
/*** check the password is the correct length ***/
elseif (strlen( $_POST['password']) > 20 || strlen($_POST['password']) < 4)
{
    $message = 'Incorrect Length for Password';
}
/*** check the username has only alpha numeric characters ***/
elseif (ctype_alnum($_POST['username']) != true)
{
    /*** if there is no match ***/
    $message = "Username must be alpha numeric";
}
/*** check the password has only alpha numeric characters ***/
elseif (ctype_alnum($_POST['password']) != true)
{
        /*** if there is no match ***/
        $message = "Password must be alpha numeric";
}
else
{
    /*** if we are here the data is valid and we can insert it into database ***/
    $username = filter_var($_POST['username'], FILTER_SANITIZE_STRING);
    $password = filter_var($_POST['password'], FILTER_SANITIZE_STRING);

    /*** now we can encrypt the password ***/
   // $password = sha1( $password );

    /*** connect to database ***/
    /*** mysql hostname ***/
    $mysql_hostname = 'localhost';

    /*** mysql username ***/
    $mysql_username = 'abcdefg';

    /*** mysql password ***/
    $mysql_password = 'abcdefg';

    /*** database name ***/
    $mysql_dbname = 'abcdefg';

    try
    {
        $dbh = new PDO("mysql:host=$mysql_hostname;dbname=$mysql_dbname", $mysql_username, $mysql_password);
        /*** $message = a message saying we have connected ***/

        /*** set the error mode to excptions ***/
        $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

        /*** prepare the select statement ***/
        $stmt = $dbh->prepare("SELECT  username, password FROM user 
                    WHERE username = :username AND password = :password");

        /*** bind the parameters ***/
        $stmt->bindParam(':username', $username, PDO::PARAM_STR);
        $stmt->bindParam(':password', $password, PDO::PARAM_STR, 40);

        /*** execute the prepared statement ***/
        $stmt->execute();

        /*** check for a result ***/
        $user_id = $stmt->fetchColumn();

        echo $user_id;
        /*** if we have no result then fail boat ***/
        if($user_id == false)
        {
                $message = 'Login Failed';
        }
        /*** if we do have a result, all is well ***/
        else
        {
                /*** set the session user_id variable ***/
                $_SESSION['user_id'] = $user_id;

                /*** tell the user we are logged in ***/
                $message = 'You are now logged in';
                echo '<script>window.location = "http://127.0.0.1/university/site/page1.php"</script>'; 

        }

    }
    catch(Exception $e)
    {
        /*** if we are here, something has gone wrong with the database ***/
        $message = 'We are unable to process your request. Please try again later"';
    }
}
?>

<html>
<head>
<title> Login</title>
</head>
<body>
<p><?php echo $message; ?>
</body>
</html>

```