Can't seem to get variables set in controllers
Close!  You want to redirect on success and let the request continue as normal on validation failure.

public function actionMyPluginAction
{
    $post = craft()-&gt;request-&gt;getPost();
    $requestModel = Micros_AuthModel::populateModel($post);

    if ($requestModel-&gt;validate())
    {
        // Yay! What I did works!

        $this-&gt;redirectToPostedUrl();
    }

    craft()-&gt;urlManager-&gt;setRouteVariables(array(
        'requestModel' =&gt; $requestModel
    ));
}