@corinnekrych instead of having a separate "AG_OAUTH2_FACEBOOK",  wdyth if we detect from the passed config that "fb" has been chosen and we use the appropriate module internally?

so the user still passes just "AG_OAUTH2" and we make the appropriate adjustment (since FB doesn't follow the spec)

Note: this is different from AGIOS-154 for user supplied oauth provider impl,  but since we are going to offer FB support internally, my suggestion is to hide this.