OAuth is an open protocol to allow secure API authorization in
a simple and standard method from desktop and web applications.

liboauth is a collection of POSIX-c functions implementing the OAuth
Core RFC 5849 standard. liboauth provides functions to escape and
encode parameters according to OAuth specification and offers
high-level functionality to sign requests or verify OAuth signatures
as well as perform HTTP requests.

WWW: http://liboauth.sourceforge.net/