Question

I am developing an online examination system using php and I wish to incorporate a feature such that anyone who intends to take a test provides an email and a unique url link shall be sent to their email. On clicking the link the user shall be logged into the system and can take a test. The url link should expire after the duration of exam is completed or in other words the link should be active only for a fixed time duration after it is first clicked.

In this case I do not require the user to provide any details except his email.

Answer 1

Use a hash like md5 or sha1 or something similar. When they fill in the form you will save their record to a database with a record id and their address. The link should have a hash of their record id so that you can easily look up the record when they click the link:

$link = "http://somedomain.com/test?id=" . md5($recordid);

Then when processing the link:

$hashId = $_REQUEST['id'];
$sql = "SELECT * FROM users WHERE MD5(id) = '$hashId'";