pfSenseHelpers.js (https://github.com/pfsense/pfsense/commit/f0136b178022cf3b04...) now contains code that intercepts clicks on anchor tags with the attribute "usepost" set. The target URL and the GET arguments are extracted from the event href attribute, and these are used to compose a new, temporary form with the previous arguments inserted as POST parameters.

Here is a simple example:

Before:

  <?php
  $id = $_GET['id'];
   
  if ($_POST) {
      if (!save_config($id)) {
          $input_errors[] = "Something broke";
      }
  }
  ?>
   
  <a type="button" href="system_something.php?id=<?=$id?>&user=<?=$pconfig['user']?> >
      <i class="fa fa-save></i>
      <?=gettext("Save")?>
  </a>

  After:
  <?php
  $id = $_POST['id'];    // $_GET was changed to $_POST
   
  if ($_POST['save']) {  // The generic if ($_POST) is now if ($_POST['save'] to detect when the form is being saved
      if (!save_config($id)) {
          $input_errors[] = "Something broke";
      }
  }
  ?>
   
  <!-- The "usepost" attribute is added to the anchor -->
  <a type="button" href="system_something.php?id=<?=$id?>&user=<?=$pconfig['user']?> usepost>
      <i class="fa fa-save></i>
      <?=gettext("Save")?>
  </a>