Authentication is required error during automated build in docker hub

I think that you should open a support ticket with them.

I am currently experiencing this issue as well with public repos depending on other public images (no auth should be required). I submitted one last week for similar issues and got the following response for that:

Our Automated Builds Team released a major update this weekend. However, this has affected the build details information when the automated build is failing. The builds that are failing are not getting proper error messages. We are working to resolve this issue as soon as possible and we will keep you updated. You can also track the status of Docker Hub Automated Builds here: http://status.docker.com/.

This may be related to them working on patching issues. I have commented on my Open issue to get more info. Opening support tickets would be the best way to notify them of the issue and get 1st hand feedback.

You can do that by going to the upper-right hand corner in dockerhub, clicking on your profile and going to "Help". Then choose the "Support" button. You may have to create an account with them.

If I hear anything back myself I'll try to post here.