Title: Make OAuth scopes configurable

Description:
It's currently hard-coded to scope but the scopes can vary widely, e.g. see Github's OAuth scopes: https://developer.github.com/apps/building-oauth-apps/understanding-scopes-for-oauth-apps/#available-scopes

cc @rgs1 @fishcakez @williamsfu99