MyBB Community Forums

Is it possible to use mybb for outh authentication on different sites?

Lets say I have a forum forum.com and it is running mybb. Another website, running some service, can offer login via 'forum.com'?

It's not supported in MyBB by default, but it's definitely possible with the use of an addon (you'd probably have to create one or get one created, haven't seen this around). Unless you mean for something like Google or Facebook, in which case you can probably find something that already exists for that.