oauth CSRF vulnerability

Summary

In the OAuth library for nim prior to version 0.11, the Authorization Code grant and Implicit grant both rely on the `state` parameter to prevent cross-site request forgery (CSRF) attacks where a resource owner might have their session associated with protected resources belonging to an attacker. When this project is compiled with certain compiler flags set, it is possible that the `state` parameter will not be checked at all, creating a CSRF vulnerability. Version 0.11 checks the `state` parameter using a regular `if` statement or `doAssert` instead of relying on a plain `assert`. `doAssert` will achieve the desired behavior even if `-d:danger` or `--assertions:off` is set.