Input a user’s age. If the user’s age is greater than, or equal to 18, request the user to enter a common access code. If the entered access code was “SECRET”, display the restricted webpage. However, if the user entered a code that was incorrect, display an error page.

You will need to use a dynamic language, PHP or JS for example.

Use serverside code because JS can be disabled.

There are many free user authentication scripts out there, but I'm afraid they are all written in PHP. If you're serious about this then you'll need to start learning PHP.

http://www.w3schools.com/php/default.asp

If you get it working though, do share.

Sigh.

Nobody actually posts code! D:

Chrishirst is right, JS can be disabled, so I'd recommend using the PHP one, but the JS one is slightly faster.

PHP: Untested, should work, though.

<?php
 $userAge = $_POST['userAge'];
 $errorPage = "error.php";
 $secretPage = "secret.php";

  if (isset($userAge)&&$userAge>18) {
    header("Location: $secretPage");
  }
  else if (isset($userAge)&&$userAge<18) {
    header("Location: $errorPage");
  }
  else {
    echo <<<AuthForm
      <form action="" method="post">
      Enter your age:
      <input type="text" name="userAge" />
      <input type="submit" value="Submit" />
      </form>
    AuthForm;
  }
?>

JS: (Tested, works)

<script type="text/javascript">
function Auth() {
  if (userAge.value>18) {
    window.location = "secret.html";
  }
  else {
    window.location = "error.html";
  }
}
</script>
<input type="text" id="userAge" name="userAge" />Enter your age
<input type="button" onclick="Auth()" value="Authenticate" />

OR If you want them to actually enter the word 'secret' as a password...


PHP: Untested, should work, though.

<?php
 $passcode = $_POST['passcode'];
 $errorPage = "error.php";
 $secretPage = "secret.php";

  if (isset($passcode)&&$passcode=="SECRET") {
    header("Location: $secretPage");
  }
  else if (isset($passcode)&&$passcode!="SECRET") {
    header("Location: $errorPage");
  }
  else {
    echo <<<AuthForm
      <form action="" method="post">
      Enter Password
      <input type="text" name="passcode" />
      <input type="submit" value="Submit" />
      </form>
    AuthForm;
  }
?>

JS: (Tested, works)

<script type="text/javascript">
function Auth() {
  if (passcode.value=="SECRET") {
    window.location = "secret.html";
  }
  else {
    window.location = "error.html";
  }
}
</script>
<input type="password" id="passcode" name="passcode" />Enter Password
<input type="button" onclick="Auth()" value="Authenticate" />

If you want I can make it so that even if they type in 'SeCRet' it will work, easily.

Just combine the two to get the outcome you want.

If the user's age is greater than 18, then display the 'secret' one. Simple. I can do it for you, too, if you can't do that yourself

JavaScript can be better to you, cause it can be easily built in an HTML and unlike PHP requires little support from hosting. Though PHP is almost the same.

Nobody actually posts code

That's 'cos this is the HTML forum and there is no HTML code can actually do what the OP requested!

LOL ta-rue...

But I figured I'd help him out