OAuth 1.0 is often implemented somewhat wrong too. I've only worked with OAuth 1.0 so I can't speak for 2.0, but the I think main problem is that social network

OAuth 1.0 is often implemented somewhat wrong too. I've only worked with OAuth 1.0 so I can't speak for 2.0, but the I think main problem is that social networks don't 100% stick to the specification, so you first have to figure out what exactly is different (at which point the guy who originally coded the thing that I had inherited had already given up), and then you either have to figure out how to get the library you're using to work anyway, or just implement it yourself. All of these tasks have pitfalls.