I agree regarding the potential broad usage for sign-in but from what I read here, I think that the app interface will need to be the developer's, not DAW's. Can anyone comment?

Remember too, what we're looking at is example code for popular web sites wrapped around OAuth 2.0. And it's consciously detached from DataFlex itself (that's why it's here in "Resources"). We are hoping that developers will expand upon what's been started and, as practical experience is gained, share their results and knowledge with the community.