Facebook OAuthConnector issues with Varnish

Trying to use Facebook OAuth Connector on Acquia Cloud and have turned on Varnish page caching. I get through the Facebook dialog boxes fine, and then when the site tries to redirect, I get taken to a screen that says:

Temporarily Unavailable

The website that you're trying to reach is having technical difficulties and is currently unavailable. We are aware of the issue and are working hard to fix it. Thank You for your patience.

When I turn off Varnish caching it seems to redirect fine and I am logged in without a problem. However, it does not create a drupal user account.

(This all works fine on acquia dev instance without varnish, and users are created fine as well)