[adimania]

From implementation standpoint, I frequently use Google Auth and a bunch of their APIs. At least for Python, I can confidently say that they are not at all painful. Yes, there is fragmentation between different oAuth providers but unless you are writing oAuth library yourself, you may not need to face these problems ever. Fyi, I am not using any oAuth lib but then I only use google auth for my app, not fb or twitter.