Git over HTTP no longer works with Kerberos

Zendesk issue: https://gitlab.zendesk.com/agent/tickets/28366 and https://gitlab.zendesk.com/agent/tickets/23103

This is the second report I've heard of Git over HTTP not working after 8.9 when using Kerberos. The web sign in continues to work but Git operations do not. Unfortunately, there aren't a lot of details available in the logs. We only see that the user is not authorized.

Can we think of anything that changed that would cause this issue?

Started GET "/group/repo.git/info/refs?service=git-upload-pack" for 127.0.0.1 at 2016-06-27 12:02:01 +0100

Processing by Projects::GitHttpController#info_refs as */*

Parameters: {"service"=>"git-upload-pack", "namespace_id"=>"puppet", "project_id"=>"repo.git"}

Filter chain halted as :authenticate_user rendered or redirected

Completed 401 Unauthorized in 76ms (ActiveRecord: 2.1ms)

Started GET "/group/repo.git/info/refs?service=git-upload-pack" for 127.0.0.1 at 2016-06-27 12:02:01 +0100

cc/ @DouweM @jacobvosmaer-gitlab Any ideas?