PHP $_GET is empty when the url has variables passed

Question

this is my first stack overflow question. I have a home page, where you can login, if you login it sends you to a login php in which you have some code that checks if login is incorrect. If that is the case this code redirects you back to home page:

header("Location: ".SERVER_ADDRESS."home?error=invalid_login");

Now you are back on the home page but the url variable is not set. It does not show in a var_dump(parse_url($_SERVER['HTTP_REFERER'])); or var_dump($_GET);

This is my index.php file:

<?php

session_start();
require_once("config.php");

if(!(isset($_GET['page']))) { // redirect to main page 
    
    header("Location: ".SERVER_ADDRESS."home");
    
} else {
    
    $mp = new MainPage($_GET['page']); // redirect to given page
    
}

?>

If you go try login again with wrong credentials and do the same redirection process it will now show the variable. Same thing happens if I were to refresh the header after few seconds.

I seem to not understand why the home page would not show the variable straight away, I just want to use the variable for an if statement that would print an extra invalid login message.

I am using wampserver64 for localhosting.

My .htaccess looks like this:

Options FollowSymLinks
RewriteEngine On
RewriteRule ^([0-9a-zA-Z\-\#]+)/?$ index.php?page=$1 [L]

EDIT: CBroe's answer helped me, my htaccess did not have a QSA flag

Your rule matches on home, and rewrites the request to /index.php?page=home. You need to add the QSA flag - query string append - to get the new query string you are creating there, merged with any existing one. — C3roe
– C3roe, Commented Mar 30, 2022 at 6:08
That alone would not explain how it works the second time or after a refresh though. Maybe you have an additional caching issue. And # in your rule pattern character class is pretty superfluous by the way, you will never encounter that character in a URL path. (RewriteRule only matches against the path component of the URL.) — C3roe
– C3roe, Commented Mar 30, 2022 at 6:10
It does rewrite to /home but the second time that is also the case, which could mean that it could potentially be a caching issue? This is a var_dump(parse_url($_SERVER['HTTP_REFERER'] after the initial login: 'scheme' => string 'http' (length=4) 'host' => string 'localhost' (length=9) 'path' => string '/gra/home' (length=9) after second time: 'scheme' => string 'http' (length=4) 'host' => string 'localhost' (length=9) 'path' => string '/gra/home' (length=9) 'query' => string 'error=invalid_login' (length=19) — SHNXG
– SHNXG, Commented Mar 30, 2022 at 12:00
This page must not be resolved by a comment and an edit of the question. SHNXG or @CBroe should post an answer so that this page is resolved officially/properly. (Also, all comments containing relevant question details should be removed. All irrelevant comments (including mine) should be removed.) — mickmackusa
– mickmackusa ♦, Commented Mar 30, 2022 at 23:09

C3roe · Accepted Answer · 2022-03-31 06:07:03Z

1

Your rule matches on home, and rewrites the request to /index.php?page=home.

You need to add the QSA flag - query string append - to get the new query string you are creating there, merged with any existing one.

answered Mar 31, 2022 at 6:07

C3roe

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