How to keep already-set GET parameter values on form submission?

You can add two hidden fields in the form on the first target site, blabla.php in your case:

<form ...>  <input type="hidden" name="name" value="<?php echo htmlspecialchars($_GET['name']);?>">  <input type="hidden" name="lName" value="<?php echo htmlspecialchars($_GET['lName']);?>">  <!-- rest of the form here --></form>

For a dynamic solution, use a foreach loop:

<?phpforeach($_GET as $name => $value) {  $name = htmlspecialchars($name);  $value = htmlspecialchars($value);  echo '<input type="hidden" name="'. $name .'" value="'. $value .'">';}?>

You may consider locking the dynamic approach down to a list of known possible keys:

<?php$keys = array('name', 'lName', ...);foreach($keys as $name) {  if(!isset($_GET[$name])) {    continue;  }  $value = htmlspecialchars($_GET[$name]);  $name = htmlspecialchars($name);  echo '<input type="hidden" name="'. $name .'" value="'. $value .'">';}?>

A simpler solution to keep the URL unchanged by using http_build_query

 <form action="<?php echo $_SERVER["PHP_SELF"] . '?'.http_build_query($_GET); ?>" ...   ..  ..

There are different ways to do this. All of them write the parameters they receive into a file, memory, or a database and retrieve them later with a key

The easiest method is something like a session variable: http://php.net/manual/en/features.sessions.php

The main setup is something like this (caution: that is unsecure code, make sure you only add session variables you want to keep, and sanitize user input!):

<?phpsession_start();foreach ($_GET as $key=>$value) {    $_SESSION[$key]=>$value;}?>

and now, as long as the user does not close the browser, you can access these variables with $_SESSION[varname];