I work on web applications and as you know, having an administrator panel is a must in most cases. We can see that a lot of web applications have a specific login page for administrators in which there is a form (usually POST method) that admins can use to login their panel.

But because the field names are known, a hacker can attempt to crack the passwords even if some security methods are implemented.

So what is the problem with a simple GET key (as username) and its value (as password)? Why it's not used a lot or at least, is not suggested in many articles?

For administrators, user-friendly login pages are not really needed! Data will be logged in both cases (GET/POST) if there is a MiTM attacker.

But using this method, fields will be unknown expect for admins themselves.
 Here is a sample PHP code:

"category.php": (A meaningless page name)

<?php
if (isset($_GET['meaningless_user']) && $_GET['meaningless_word'] == "something"){
    session_start();
    $_SESSION["user"] = "test";
    header('Location: category.php');   // Redirect to same or other page so GET parameters will disappear from the url     
} else {
    die(); // So it'll be like a blank page
}
?>


This would store the login link with password and username in the browsers history. It could also be accidentally be captured by things like firewall logs, that wouldn't capture post variables.