从DocuSign API请求访问令牌时收到400错误的请求消息

我可以通过使用链接 https：//developers.docusign来生成docusign网站的访问令牌.com / oauth-token-generator

但是，当尝试使用c＃代码在我们的系统中获取访问令牌时，却收到消息（远程服务器返回了错误：（400）错误的请求。）

But when try to get access token in our system using c# code then getting message (The remote server returned an error: (400) Bad Request.)

我遵循以下链接中提到的身份验证过程。

I follow the authenticate process mentioned in below link.

https://developers.docusign.com/esign-rest- api / guides / authentication / oauth2-code-grant

我能够获取验证码。我使用了此身份验证代码来访问API（ https://account-d.docusign.com/oauth / token ）。

I able to get authentication code. I used this authentication code to hit API (https://account-d.docusign.com/oauth/token).

下面是我的代码示例

string integrationKey = "key removed";
string secretKey = "key removed";
var httpWebRequest = (HttpWebRequest)WebRequest.Create("https://account-d.docusign.com/oauth/token");
httpWebRequest.ContentType = "application/x-www-form-urlencoded";
httpWebRequest.Method = "POST";
string apiStoreConsumer =    "removed";
 httpWebRequest.Headers.Add("Authorization", "Basic " + apiStoreConsumer);
 using (var streamWriter = new StreamWriter(httpWebRequest.GetRequestStream()))
  {
   string input = "authorization_code&authorization_code= <authentication code goes here>;

   streamWriter.Write(input);
   streamWriter.Flush();
   streamWriter.Close();
 }

WebResponse response = (HttpWebResponse)httpWebRequest.GetResponse();

查询：

为什么会出现400错误？
我们是否有访问令牌的到期时间，如果是，那么需要多长时间？
身份验证代码是否对每个请求都有效？

Why am I getting 400 error? Do we have any expiry time for access token, if yes then how long? Does authentication code get change for every request?

请帮助我。

谢谢！