title: Custom method on form submission with Umbraco Forms
body: <p>What I'm trying to achieve is to customise what happens during the <code>HttpPost</code>/<code>OnSubmit</code> of a form created with <a href="https://umbraco.com/products-and-support/forms/" rel="nofollow noreferrer">Umbraco Forms</a>, whilst still maintaining the default behaviour of the form and any subsequent workflow. </p>
  
  <p>In my specific scenario, I need to be able to analyse the input of the form and based on that input I will send the user to a different "thank you" page, whilst also storing some elements of the originally submitted form in TempData.</p>
  
  <p>I've tried the following:</p>
  
  <ul>
  <li><p>I've tried to create a DocType controller (<code>RenderMvcController</code>), but this only allows you
  to override the HttpGet, and not Post.</p></li>
  <li><p>I cannot use a SurfaceController as I lose the functionality of the
  module, Umbraco Forms. </p></li>
  <li><p>I've tried to use a custom workflow, but this runs asynchronous to
  the user's journey and I cannot change their experience.</p></li>
  </ul>
  
  <p>There isn't much useful documentation available for this at all and I'm finding this task more difficult than I expected it to be.</p>