byte[] bytes = Encoding.UTF8.GetBytes("AALCBSDVJPDFWGAUIKZZCUYVOGPCUO");
 string base64String = Convert.ToBase64String(bytes);

 signer.Certificate = certificate;         
 signedData.ContentEncoding = CADESCOM_CONTENT_ENCODING_TYPE.CADESCOM_BASE64_TO_BINARY;
 signedData.Content = base64String;

 signedMessage = signedData.SignCades(signer, CADESCOM_CADES_TYPE.CADESCOM_CADES_BES, false, CAPICOM_ENCODING_TYPE.CAPICOM_ENCODE_BASE64);
 signedData.VerifyCades(signedMessage, CADESCOM_CADES_TYPE.CADESCOM_CADES_BES, false); 

//get random data
            var httpWebRequest = (HttpWebRequest)WebRequest.Create("https://demo.fashion.crpt.ru/api/v3/auth/cert/key");

            httpWebRequest.Proxy.Credentials = System.Net.CredentialCache.DefaultCredentials;
            httpWebRequest.ContentType = "application/json";
            httpWebRequest.Method = "GET";

            var httpResponse = (HttpWebResponse)httpWebRequest.GetResponse();
            using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
            {
                result = streamReader.ReadToEnd();
            }
            jsonSettings.Formatting = Formatting.Indented;
            RandomData randomData = JsonConvert.DeserializeObject<RandomData>(result, jsonSettings);

            byte[] bytes = Encoding.UTF8.GetBytes(randomData.data);
            string base64String = Convert.ToBase64String(bytes); //random data to base64 string

            signer.Certificate = certificate;
            //signer.Options = CAPICOM.CAPICOM_CERTIFICATE_INCLUDE_OPTION.CAPICOM_CERTIFICATE_INCLUDE_END_ENTITY_ONLY;
            
            //sign by certificate
            signedData.ContentEncoding = CADESCOM_CONTENT_ENCODING_TYPE.CADESCOM_BASE64_TO_BINARY;
            signedData.Content = base64String; 
            signedDataStr = signedData.SignCades(signer, CADESCOM_CADES_TYPE.CADESCOM_CADES_BES, false, CAPICOM_ENCODING_TYPE.CAPICOM_ENCODE_BASE64);
            signedDataStr = Regex.Replace(signedDataStr, @"\n|\r", "");

            //get auth token
            var httpWebRequestSign = (HttpWebRequest)WebRequest.Create("https://demo.fashion.crpt.ru/api/v3/auth/cert");

            httpWebRequestSign.Proxy.Credentials = System.Net.CredentialCache.DefaultCredentials;
            httpWebRequestSign.ContentType = "application/json";
            httpWebRequestSign.Method = "post";
            
            //post data
            message.uuid = randomData.uuid;
            message.data = signedDataStr;
            string json = JsonConvert.SerializeObject(message);

            using (var streamWriter = new StreamWriter(httpWebRequestSign.GetRequestStream()))
            {
                streamWriter.Write(json);
            }

            var httpResponseSign = (HttpWebResponse)httpWebRequestSign.GetResponse();
            using (var streamReader = new StreamReader(httpResponseSign.GetResponseStream()))
            {
                result = streamReader.ReadToEnd();
            }