title: Slim 3 prevent form resubmission
body: <p>Currently after a user adds something with <code>/add</code> I will have it run a function and redirect to <code>/add</code> with a message. </p>
  
  <pre><code>$app-&gt;post('/add', function ($request, $response) {
      // Define and add query parameters
      $params = $request-&gt;getParams();
      new Add($params);
  
      // Add the new entry
      Add::newEntry();
  
      // Return View
      return $this-&gt;view-&gt;render($response, 'add/add.twig', [
          'add' =&gt; true
      ]);
  });
  </code></pre>
  
  <p>How would I make it so after Slim redirects a user it prevents the form from submitting again upon a refresh?</p>