Added option to disable automatically resolving callback url

[mattmccarty]

In regards to https://github.com/jaredhanson/passport-oauth2/issues/51, this is what I'm proposing: An option (just like passReqToCallback) to disable auto resolving callback urls, though, it will be passed in the call to passport.use() instead of the strategy options.

[mattmccarty]

Actually, it makes more sense to add it to the strategy settings. I've updated the pull request.

[mattmccarty]

Any update on this?

[rwky]

@mattmccarty if you make a PR against https://github.com/passport-next/passport-oauth2 is will get looked into.