There are currently two modules available Zendesk and Drupal-support sites:
Remote authentication module allowing for single sign-on between Zendesk and Drupal-supported sites, so that users logged into your site are automatically logged into your Zendesk.
Zendesk Feedback Tab
Easily add a Zendesk feedback tab to your Drupal site. Configure the tab online and use Drupal permission to determine if the tab is shown for anonymous users, authenticated users, or a restricted role.