Github doesn't, but Microsoft has shifted from a software licensing company; they make most their money off of subscription services now I believe, but never forget that they added ad tracking and advertising options to their operating system, and only after a lot of pressure do they start your new system up with asking about what privacy invasions you will permit for the sake of advertising.
Thanks for the feedback. We've added those platforms that we believe are most popular for the majority of web users. In my opinion, the best solution would be something similar to what Solid (https://solid.mit.edu/) proposes. Unfortunately, they don't have much traction yet.
At the very least offer Github or Ubuntu One or something as a single sign in option for those who don’t trust either your database or BigCorp