when a user signs up on my website,they get a similar link;

website.com/confirm_register.php?id=2d3ca81caf061fe873b16b98573ebd10

after clicking the link ,they are directed to a similar link website.com/alerts.php

but the alerts.php checks for authentication,here is the code below;
PHP Code:
require("inc/conn.php");
session_start();


if(!isset(
$_SESSION['username'])) {
    
header("Location: login.php");

as you can see the code above ,only checks for session,i also want to check if a user came direct from clicking the verfication link so that they can access automatically without having to login again

cheers