Ask HN: about Oauth integration

I tried to implement some Oauth from 3rd party services (Linkedin, Facebook, Google, Soundcloud) and I'm asking if I'm the only one to take hours/days to make it well for each.

- How long did you take to implement each of them? - How many different Oauth specs you encoutered? - Each time it is different or after practicing few it is ok for the other dozens ones?