I just finished putting together my t3db0t:accounts-invite package, which allows you to easily allow or deny account creation even for oauth services. Live demo/explanation here: accounts-invite-demo.meteor.com
Every beta invitation system for Meteor I have seen just uses password-based accounts, whereas I wanted invited users to be able to create accounts with any service.
This turned out to involve a crazy amount of hackery; the full explanation is at the link above. This is arguably a workaround to just adding finer-grained control to the
accounts core package, but for now I find it super useful.
Comments and PRs are welcome. PLEASE let me know if you have any problems or find any bugs. At the moment I’m not aware of any security holes, but definitely report any!