An example of how to authorize Nylas from .Net

NylasAuthResponse.cs

public async Task<ActionResult> NylasAuthenticationResult(string code)
        {
            using (HttpClient httpClient = new HttpClient())
            {
             
                // tried as x-www-form-encoded
                var postData = new List<KeyValuePair<string, string>>();
                postData.Add(new KeyValuePair<string, string>("client_id", "cf7jhxlkkvimkxvd2vnkkzci"));
                postData.Add(new KeyValuePair<string, string>("client_secret", "your_secret"));
                postData.Add(new KeyValuePair<string, string>("grant_type ", "authorization_code"));
                postData.Add(new KeyValuePair<string, string>("code ", code));
                
                HttpContent content = new FormUrlEncodedContent(postData);

                var authorizeResponseMessage = await httpClient.PostAsync("oauth/token", content).ConfigureAwait(false);

                var authorizeResponse = authorizeResponseMessage.Content.ReadAsAsync<NylasAuthorizeResponse>().Result;
            }

            return null;
        }