I do wish Curl supported OAuth 2.0 out of the box - I would then drop all REST clients in a jiffy.
I am interested in this because we're starting to work on a project where these two ingredients will come together.
After looking at the cURL site, it looks like someone had the need and the will to bake in kerberos, so why not OAuth? Then I looked at the OAuth specs. It would be quite an undertaking for sure, but it could be good :-)