After a few days of playing around with oauth-php library and a weekend of fighting with it and wrapping my brain around OAuth workflow, I finally added OAuth-base login to UserBase.
Right now only module for Meetup is ready, but most of the logic is in generic OAuth class so I hope other modules will come soon. I already did hit problems with other providers like Twitter and LinkedIn which have some troubles with generic OAuth so it’s not going to be an easy flight.
Standards are good anyway, even if they are not supported uniformly across the board (they never are).