Ryan Adams shows us how to get Active Directory authentication on Linux using Samba and PAM:
Back to our question at hand. Since the preview just got released I have not had a chance to test this out with SQL Server. However, you can use Active Directory accounts with Linux and Unix by using Samba and PAM. I see no reason why this implementation would not also work with SQL Server on Linux, but again I have not yet had a chance to test this out. Since I already have some written installation instructions, that’s what I am providing here.
Chrissy LeMaire, in the comments, shows how to do it in OpenSUSE. She also has a brand new blog post on the topic.