Where is the OAuth2.0 Authorization Code stored?

Question

I'm developing a C# application that needs to contact a web-based API. When contacting the API, the first thing it does is try to get an authorization code from an authorization server. Using RestSharp, my code is this:

        static string GetAuthCode(string authUri, string clientId, string scope, Guid state, string callbackUri)
        {
            var client = new RestClient(authUri);
            var request = new RestRequest("", Method.Post);

            client.Options.MaxTimeout = -1;
              
            request.AddParameter("client_id", clientId);
            request.AddParameter("response_type", "code");
            request.AddParameter("scope", scope);
            request.AddParameter("state", state);
            request.AddParameter("redirect_uri", callbackUri);
             
            RestResponse response = client.Execute(request);

            if (response.IsSuccessful)
            {
                string code = HttpUtility.ParseQueryString(response.ResponseUri.Query).Get("code");
                return code;
            }
            else
                throw new Exception(response.Content);
        }

When I call this method, the response is successful, however I was expecting that the resulting authorization code would be appended to the ResponseUri property of the response (in its Query property). But it's not. The ResponseUri property is set to the authorization Uri (authUri). Am I looking in the wrong spot for the authorization code? Where can I find the actual authorization code?

Answer 1

It should be in the query parameters:

If the resource owner grants the access request, the authorization
server issues an authorization code and delivers it to the client by
adding the following parameters to the query component of the
redirection URI using the "application/x-www-form-urlencoded" format, per Appendix B:

4.1 Authorization Code Grant - 4.1.2 Authorization Response