Pay with Amazon in "Shopping cart block"

/**
 * Implements hook_commerce_line_item_summary_link_info().
 */
function commerce_cba_commerce_line_item_summary_link_info() {
  $cba_widget_settings = variable_get('cba_widget_settings', array());
  $checkout_button = commerce_cba_amazoninlinewidget('checkout', $cba_widget_settings);

  return array(
    'checkout_cba' => array(
      'title' => drupal_render($checkout_button),
      'attributes' => array('rel' => 'nofollow'),
      'weight' => 5,
      'html' => TRUE,
      'access' => user_access('access checkout') && user_access('access checkout by amazon'),
    ),
  );
}