Octokit OAuth Token Ruest

gistfile1.cs

var gitHubClient = new GitHubClient(new ProductHeaderValue("Test App", "0.0.0.1"))
{
    Credentials = Credentials.Anonymous
};

var content = new FormUrlEncodedContent(new Dictionary<string, string>
{
  {"client_id", ClientId },
  {"client_secret", ClientSecret },
  {"code", responseParameters["code"] },
  {"state", state }
});

var response = await gitHubClient.Connection.PostAsync<AccessToken>(new Uri("https://github.com/login/oauth/access_token", UriKind.Absolute), content, "application/json", "application/x-www-form-urlencoded");

return new Credentials(response.BodyAsObject.Token);