As well as being open source, Impressory tries to be open about working with other systems rather than trying to own everything itself. This extends all the way to logging in — Impresssory is quite happy with the idea that you might want to log in directly from your CMS (Moodle, Blackboard), or use some other identity service (Twitter, GitHub account, etc) rather than using a username and password
Just because you log in with Twitter doesn’t mean you necessarily want Impressory posting to Twitter for you.
Impressory