I am trying to add additional submit buttons to the webform to navigate between different steps. I have added button like below:

    function mymodule_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
    if($form_id == 'mywebform_id') {
        $form['actions']['submit_button_step_1'] = array(
    	  '#type' => 'submit',
    	  '#value' => t('Go to Step 1'),
    	  '#submit' => array('custom_navigation'),
    	);
    	$form['actions']['submit_button_step_2'] = array(
    	  '#type' => 'submit',
    	  '#value' => t('Go to Step 2'),
    	  '#submit' => array('custom_navigation'),
    	);
    }
    }
    function custom_navigation(&$form, \Drupal\Core\Form\FormStateInterface $form_state) {
      $value = $form_state->getValues();
      //echo '<pre>';print_r($form['actions']);echo '</pre>';exit;
    }

But, I'm using same custom submit handler both the custom buttons. How I identify which button has clicked by user?