This is not necessarily a Sign IN with Twitter, but a SIGN with Twitter feature.
The best way to explain it is this, if you have a petition, and you want people to SIGN the petition with their twitter account (to prevent fraudulent activity). You would probably want them to authenticate with Twitter, then use their username and store it in your own database as a “SIGN,” is that right?
I am doing this in Ruby/Rails, and I will work toward that end, I just want to make sure I am thinking properly about this. When you use an “authenticate with twitter” feature, how easy is it to “Keep me signed in?”